We had the same problem, trying to insure our Marea 155 in my girlfriends name (24, no accidents, 2 years no claims). No-one would touch it till she hit 25. I swapped our insurances around and TSB (Churchill) agreed to put her on as a named driver although it was against their policy. Since then I've heard good quotes from Adrian Flux, they specialize in high risks (Custom, Modified, Yanks etc.). I haven't got a number to hand, but they advertize in quite a few magazines. Give 'em a try and let us know how you get on.
Cheers and Good Luck
The Mighty