Any gearbox shop worth their salt will be able to rebuild it for you, the problem is getting parts. When I stripped mine down I found lots of things I needed to order, A shop would need to inspect it then give you a list to track down.
Or you could short cut this process and just order the following from either burtons or bearing kits in the UK and take them to a shop in advance, none of these items are a waste of money when rebuilding a gearbox because it's better to do it once while it's all apart.
1st to 4th brass synchro rings
Rebuild kit (all bearings and seals)
1st gear - either the original ratio or the shorter 2.98:1 (which is more expensive as you need to replace the laygear)
2nd gear
The rest should be fine unless there was catastrophic damage / abuse. The gearbox I opened and inspected recently had a hard life, massive wear on first and second gears/synchros but all the blocker bars and springs were still good.
Edit - Oh and the sandwich plate is a pig of a thing to get apart, that's the most difficult part of the whole disassembly.