There are dozens of issues that had second and third printings, but I don't really consider those "variants", just later printings. I think the first 37 issues all got at least a second printing (originally or via toy inserts).
Check out Atomic Avenue. It's created by the same people and uses the same database as the comic tracking software "Comicbase". They list pretty much every known issue, reprint, and variant, including toy inserts/reprints.
http://www.atomicavenue.com/atomic/T...x?TitleID=4539
It's a great site for researching questions like this (or buying issues too).
