I've got a group of 13 VIC-20 carts, including Aggressor and Tutankham, over on eBay. All have their boxes in decent condition, and most have instruction manuals too. The auction has a reserve price, but I've adjusted it to $22 (a buck over the current high bid), so don't worry about whether you'd meet it or not.

http://cgi.ebay.com/Lot-13-Commodore...89124347025520