The United States Mint is working diligently with current and potential blank suppliers to increase the supply of bullion coin blanks, so it can offer to the public the proof and uncirculated versions of American Eagle silver, gold, and platinum coins in 2010.
I remember reading that U.S. gold coins must be minted from newly mined American gold by law. I don't know whether that applies to silver or platinum, but I wonder if it's a factor in the shortage of coin blanks.