Bristol GS, and CabAir are the only 2 I know of in the UK.
I've heard a lot of good things about Bristol
HAI Bristow do have hourly rates on there web site so maybe, depending on how long it takes, you may need a student visa.
I'm off out to them in a 5 weeks, so if you email me I can ask for you, or give them a call, I've found them really helpfull.
Peter.
MSN
[email protected]