Try www.paint4models.com but don't download it, just launch it (if you download it you get a different chart that's not interactive). This is the most comprehensive cross-referencing chart I've found, and you can find the paint numbers for many different brands, from Tamiya to Testors to Humbrol to the actual Federal Stock numbers. If you find the Testors color it will also show the same color from all the other brands.