Most in the UK should be fairly low mileage as they were only made in 2002. Mine has just ticked over 25K but it was only on 10K when I bought it 18 months ago - it's my everyday drive.
Try looking for one of the the cars that were sold new by Xtreme. Mine is one of these and wasn't registered until June 2003. I've seen a few other 03s with similar number plates so there must be more out there. Not likely to see many for sale until summer though so I'd just keep an eye out til then.
Cracking car the GT-A, especially now ECUTEK is available. Getting mine done Friday at The Racing Line in Halifax, can't wait