Try testors model master spray cans for Panzer gray and Afrika mustard, and for the Sherman green the Tamiya green (maybe 66?) is a very good match. The Afrika mustard is a bit dark, so if it's small enough to look good brush painted I'd go with Testors dunkelgelb '43, but that's pretty much only available in acrylic anymore. The enamel is still out there, but very hard to find and expensive when you do. I saw one jar on ebay for $18, a bit too rich for me. But the acrylic is readily available for four or five bucks a jar.