Kevin Taylor may look like your average green grocer, with his stall of neatly stacked boxes of broccoli, carrots and strawberries. But he has developed a reputation for being somewhat of a detective. His clients - not suspicious spouses or shady lawyers - are chefs and bartenders at some of the world's top establishments looking to get their hands on the most elusive of exotic ingredients.

Taylor's family business, Taylor and Son, was founded in the early 1900s in the street markets of London's Islington district. In the 1970s and '80s, it started supplying directly to local restaurants. Now, chefs and bartenders across London and beyond phone Taylor daily for fresh goods from as far afield as Colombia, Kenya and the Caribbean.

One of Taylor's long-standing clients is Nightjar, voted the third best bar in the world in The World's Best 50 Bars 2016. Nightjar is known for its cutting-edge, creatively presented cocktails using unfamiliar ingredients such as North African alligator peppers, a Central American herb called epazote, a South American citrus fruit called lulo, and buffalo worms - crunchy edible beetle larvae. For the bartenders here, Taylor has sourced an incredible array of items, including Asian staples that are considered exotic in the West, such as galangal, longan and osmanthus.

"When chefs and bartenders ask if I can find a certain ingredient, I ask around with my suppliers, who get in touch with their suppliers, who talk to their guys … It's a network that stretches all across the world," Taylor says. "The bartender at Nightjar asked me for baobab pods, these big green tree pods from Africa. But no one was importing them. I managed to track down a supplier in Kenya, who put a box of the pods on a pallet with other produce being exported."

Nightjar now uses candied pineapple and baobab syrup in their Punch A La Burroughs, which combines tequila, Inca berry infusion, lime juice, orange blossom liqueur, bergamot bitters, green rooibos matcha and Mercier Brut Champagne.

Even for the world's biggest hotels, sourcing exotic ingredients can rely on a loose and informal network.

"I travel and read a lot. That's where I get ideas in sourcing various ingredients. Also, we've built up a network of suppliers, friends and chefs who share if they've found something new or rare with me," says Uwe Opocensky, executive chef at the Mandarin Oriental, Hong Kong.

It's also part of executive sous chef Robin Zavou's role to find new and rare ingredients, and do the in-depth research with suppliers on locating them. Some ingredients don't come through the usual import networks at all, however.

"A chef asked me to find a special kind of corn from Peru," Taylor says. "I know a Peruvian guy who goes home five or six times a year to bring back tourist stuff to sell. So I asked him to get me the corn. Unfortunately, he was stopped at the airport in Barcelona. I'm sure he also stuffs his socks with fruit when coming back from his trips."

Still, the effort in trying to locate and import these rare ingredients is worth it. Opocensky points out that today's diners are adventurous, and are always looking for new things to try, while journalists are also always on the hunt for new things to report on. The interest created by these exotic ingredients drives chefs to feature them on their menus.

"Some locations, such as Hong Kong, don't offer many local ingredients. Also, our particular clientele are world travellers, so there are indeed certain expectations," he says.

For Nightjar, which has a reputation for the avant-garde, keeping the menu fresh is critical. Edmund Weil, owner of Nightjar, says he never misses an opportunity to visit the local market when he travels to anywhere from Seoul to Marrakesh to see if he can find interesting ingredients with unusual flavour profiles. His bartenders take on guest roles at other bars and enter mixology contests, which helps to inspire them in many ways, including in using new ingredients.

Often, though, it's not whether you can find an unusual ingredient, it's whether you can source enough of it all year long. Some quite common ingredients, such as blood oranges, are only available three months of the year, Weil says, so they can only use these in their seasonal menu.

"Thanks to globalisation, sourcing seasonal items is getting easier, though," he says. "And we have found that some freeze dried fruits work well in cocktails. The taste comes through just fine, and you're going to be shaking them around anyway."

Freeze drying is just one way of preserving hard-to-find seasonal produce. Nightjar also turns ingredients into bitters, such as Szechuan buttons, the edible buds of acmella oleracea, which give a numbing sensation akin to China's much-loved Szechuan pepper. "Chewing the flowers is a bit like chewing a battery," Weil says.

They submerge the buds in high-strength, neutral-grain alcohol, and put them through a sous vide - cooking at low temperatures in an airtight bag in a water bath - process, to make their "electric bitters".

The bitters add that little something extra to Nightjar's martinis. Weil says it took them three months to get enough flowers to make 10-litre batch of the bitters as only one person grows these plants in Britain, and a few in Holland.

While supply may be limited, most ingredients are, in today's globalised world, able to cross borders quite easily. Opocensky says he hasn't had problems sourcing items.

"There are only minor restrictions in Hong Kong, so I have never encountered any issues," he says.

Critics dismiss exotic ingredients as being gimmicky. Weil says that while newly devised cocktails at Nightjar can indeed sometimes "start out a little gaudy", they make sure that any garnishes add something sensory to the overall experience rather than being just pure decoration.

"You can go anywhere to get a great drink, but we've become famous for that extra element, our 'Instagrammability'," Weil says.

"People are interested in having unique experiences - be it bungee jumping or coming to Nightjar - and these experiences have become a status symbol."