I think I've seen more Gold/silver ones for sale than just silver...but the gold is just an add-on to the silver I guess.
id love to know the count
Casascius posted once that there was an almost even split between the all silver and the gold painted ones. And there's 450 or 486 total 10
BTC coins depending on the site you look at (
http://casascius.uberbills.com/ or
http://casascius.appspot.com/ I'm not sure which is the correct count)