Ahh... so you ended up with at one! I saw it on e-bay and was tempted to have a nosey as it was local to me.
All the mechanical bits you need you should be able to source from DC Supercars, http://www.dcsupercars.com/
Give them a ring and talk to Dave Harrison.
Then if you're after any original pars have a look on Eurospares web site (and take out a 2nd mortgage!) http://www.eurospares.co.uk/
Although a lot of the parts were just general bits (i.e. Fiat) and over on LamboReplica we started putting together a list of what was made by whom, so that you could try and source parts cheaper from the likes of e-bay:
Good luck with the rebuild and please post lots of photos as we'd all love to see how it goes
Note: Not Harrision, another one. Bizarrely there seem to be a lot of Dave's around the Countach replica scene!