Treehouse-kids make them as figures for a play set. you can also get them in randome swarm packs made for the aliens play set.
http://www.treehouse-kids.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=ACPS1&Category_Code=0200
It takes a little work to clean the mold lines up from these guys since they are not made out of a hard plastic. but a file cleans the lines off just fine.
I am right now converting one of my pulse rifle marines to hold a motion tracker I made out of greenstuff.
since I wanted to use these in table top gaming I had to cut off those cheap army men bases they come made on and attach them to rounded bases made from small caps that I glued meshing to.