The parts are available from lambostuff and probably other suppliers..
2. hand gearboxes i think is pretty hard to find. eurospares.co.uk have an engine spare with gearbox i think.. You could try to send them an email..
I would fix your own gearbox, in that way you know what your dealing with..
The 2nd gear syncromesh is an known urraco problem. I changed the gearoil but the 2nd gear is hard when cold, but when its wam it works like a charm.. I just skip 2nd and go right from 1. to 2nd when the gearoil is cold..

Daniel