hello mate, ebay has a fair few - Triumph keyless fuel caps and "I believe" KTM ones fit - I can speak from experience that the Triumph ones fit (nice and snug fit in the tank venturie).
The DHM ones are quite resonably priced (about 30 squids from most bike shops) or http://www.intobikes.co.uk/products?id=001218&src=fro and if you're quick - today these guys are having a 10% off day http://www.demonbikes.com/more/on/details/6682 otherwise just take a look on ebay matey.