There are 2 that spring to mind
http://www.northoffroad.co.uk/http://www.whitbread-offroad.co.uk/rollcages.htmlThere are quite a few adverts in the back of the mags.
There is one company i have seen, can't remember which one, but am sure all of them will make it to your spec, anyway this company did a roll cage that had seatbelt mounts, and the roll bar by the bulkhead actually replaced the front hoop. The rear hoop sticks attached to the roll bar. I was very impressed by that. Quite easy for them to do, but its the little things that make it, like having a hi-lift mount, or a spare wheet mount.
Depends what you want.
I hope you have some ideas about what it is you are after.
Good luck