Konigseder and Startech made specific front splitters which look great, but at a huge cost, and not readily available. Other than these, I haven't seen any other splitters fitted to the NA Crossfire - especially anything in the UK.
I have also wondered if any other car splitters could be modified relatively easily to fit our cars. I have seen a US member use a Seat Cupra front splitter on the crossfire which looked quite good, he has a thread on the forum that provides a full "how to" guide. From experience with other vehicles I would say something from VW range could be made to fit - they are pretty easy to work with. Maybe something this:
VW GOLF MK4 1997-2003 * NEW * FRONT BUMPER SPOILER on eBay (end time 19-Dec-10 16:46:14 GMT)
I'd be very interested to hear from anyone who has sucessfully fitted something different to the front of their Crossfire.