Order them direct from the Mint. You'll want coins from all the Mints, of course.

So I'm working in a small town in Ohio Amish country, 30-some miles from Cleveland, rural country. A man comes into the library (Yankee, not Amish) and asks about what appears to be a silver coin he found in the barn.

I look at it and realize it's old -- it's hand stamped out. You guessed it: a tetradrachma piece from the time of Alexander the Great.

The guy decided that he'd best put it in his safe deposit box....