I actually did a bit of research and found a place in America that started making tips specifically for the 335's (www.dimisatips.com). The Dimisa tips were rated very high quality so I ordered them and got delivery in about a week.
When I got the tips they were indeed good quality, but due to a slight redesign they did, they appeared to long. I queried this but was told any decent exhaust place will be able to adapt them to work. I went to Tyrespot who put the car up on a ramp and called me through to have a look. The rear passenger side has a flapper valve just before the tip and if a weld was done from there, it would stick out just over 50mm past the bumper!
After numerous emails with JP at Dimisa, he was insistant it can be done and has been on hundreds of 335's and I should try elsewhere.
AAS exhausts was close by and recommended so I went to him, he said pretty much the same thing, they are too big. In the end I got him to supply one that will fit and do the work which was done very well. Cost £150 most of which I presume was labour but the place was really busy (I had to wait 6 weeks to get a booking) and he had cars and bikes from all over the country sitting in the workshop (Saw a lovely Ariel Atom and F430 race car) so I knew I would probably pay a bit extra.
I would imagine any well reputable exhaust place would be able to do the exact same for £80 - £150, looking at the price of tips they seem to range from £20 - £50 each
I'll just sell the other tips on ebay as just normal ones for any car to get back some of the money I spent on them...