If you are so inclined, here is a website to obtain HD paints...just be aware, in these Ecological/Hard times, paints like these may be difficult to obtain in the near future, so those who need touch-up paints, may want to get a bit for fixing minor paint issues.
Adventure Harley-Davidson
While it is expensive, like Rich said E-bay is pretty good and of course you can get custom work done by MOCO custom works to have the tins done, but keep your old ones.
There are others who have a lot of experience with paint. Whatyardwork has in the past provided some very good insight on PPG who is an OEM provider of HD colors/paints, you might PM him if you feel like giving it a shot. There are some great artists who have posted here some of their superb personal works...