I would try a role playing store... "Citadel Paints" is what I use to touch up my guys and vehicles too.

http://uk.games-workshop.com/storefront/store.uk

This is a general link. It covers mainly painting the minitures... some fine detailed work and ideas that I have used on my guys. I like them because they dry fast and look great. They also have alot of colors to closely match G I Joe Figures that you want to restore.