I bought the same types of pieces from Rolco a few years ago:
http://www.rolcogames.com/search.php?runsearch=true&catid=14
They are indeed a bit big, but they look good. The tanks and subs are clones of pieces that were originally designed for the Supremacy board game. I also bought some of the Rolco rocket pieces in white: laid on their sides rather than vertically, they make pretty good atomic bomb pieces.