Why not try Spain? With all the ex-pats out there, there are plenty of accessible venues and even equipment hire, especially in the more popular areas like the Costa Blanca. Keep checking Able Magazine as well, they have holiday articles in every edition of the magazine so it's worth having a look at where they feature.
I'd recommend you try Access at Last, a really good holiday company who vet all their properties for accessibility.
www.accessatlast.com or 01772 814 555.
Good luck!!!