Cosworth211,
I think Ulitmate High also have a place at Goodwood, which might by more convenient for you than Kemble.
Western Air at Thruxton have a Slingsby T67M Firefly which is very reasonably priced per hour. I know they do aerobatics training, but I don't know whether they do the AOPA Certificate. Give them a call on 01264 - 773913, (the CFI is Barry Dyke).
I believe there is also a newly arrived specialist aerobatics outfit at Thruxton operating Pittses. Alas, I know nothing about them beyond the fact that they are there. Ask Thruxton's airfield manager; he should know about them.
Good luck!
Broomstick.