Well- I was at Target last night and found some foil wrapped chcolate eyeballs in the back by the Halloween candy. About the size of a marble. They were kinda steep- I think $2.40 for like a dozen. But I thought of your post, so wanted to let you know.
I think a place like JoAnn Fabric or a Michael's craft store would have those type of goodies. Also Party City in Chanhassen had a lot of baking related items for Halloween when I was there last year. Best of luck. It sounds like a fun project.