Hi
If you do manage to get the current wheel off then post a picture of the inside of the wheel and someone might be able to suggest an alternative.
If you are really lucky and it is a standard touring car hex then you are going to be spoilt for choice in terms of wheels and tyres.
In terms of finding a good Rc car shop in Portsmouth you are going to struggle apart from the general model shops that might have the odd kit in stock. No offence to them but they may struggle to help you with a solution.
If you are willing to travel then RC Lazy in Bournemouth and Reality Racing in New Milton (just google the names for details) are both run by racers who I am sure would be able to help.
Failing any of that if you let me know I can be at the TORCH track (details in my signature sign thingie) next weekend (22nd) and can bring some touring car wheels and see if they fit. If you are interested in starting racing yourself you ought to come and see us anyway as we have the best local track
Good Luck
Rob