The technical name would be a planchet. Most of them can go on ebay from $2-10, depending on composition and eye appeal. Also, just for future reference, American 1 cent coins are called cents, not pennies.
True, but calling them pennies is OK in my book And here's the current eBay auctions for blank cent planchets: http://www.ebay.com/sch/i.html?_nkw=blank+planchet&_sacat=253&_odkw=blank+cent&_osacat=253&_from=R40
