I may be a bit late to this party for you BUT it's worth dropping an email to Mike at Elite Shooting Centre. He does a lot of custom upgrade work on 5.1's so I'll bet you he throws away stock recoil springs like they are going out of fashion. Regularly he sells real TM spares cheap from units he's pre-upgraded so definitely worth a shot. (Also does some lovely stainless barrels which are exceptionally well priced).
