Would anyone know if it is possible to buy online T700 or high modulus carbon, in small quantities, either as dry fabric or a low/medium temp prepreg?

Soller Composites sell it as dry fabric. 

Currently the only T700 based fabric we have is our CarbonFibre +/- 45 Biaxial 300g 1m Wide

Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

It's worth pointing out that T700 is a high strength fibre, its modulus is standard (the same as T300). Strength and modulus are not the same thing.

As Warren says, our 300g biaxial fibre is T700 throughout.

I hope this helps. 

Matt Statham
Easy Composites / Carbon Mods - Technical Sales