As we know, Timpsons do replacement car keys. Spoke to my local branch last year, when I thought I had lost the spare key to my daily driver (subseqently found luckily). Went in to local branch today and explained your problem to helpful guy there. He reckons they may be able to do you a "generic" 433mhz fob programmed/chipped for a C5 Vette. He mentioned something thats done in Turkey as part of the process. He said they might or might not need to see the car to do it. I expained to him that if you do buy a replacement key(s), there is a process on the car to match the key(s) to the car.
So worth exploring with them? Said he needed the reg # of the car to take further/ couldn't say yes we can definitely do one for a C5/433mhz which is less hopeful?