They came out of a set like this (not mine):
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160594660181&ssPageName=STRK:MEWAX:IT#ht_1333wt_946

I was told that these sets are limited as it says in the listing. I was lucky and picked up a set pretty cheap couple years ago for about 10% of that listing price.