Hi there,
I have a Caltron 6 in 1 Nintendo Entertainment System cartridge for sale on eBay. It's in really really good condition (cartridge only though). If you're interested, the auction has just under 3 days left to go (it ends on July 23rd at 10:42 PST). You can find the link to the auction here:
eBay: NES Caltron 6 in 1 cartridge
Also, on a slightly related note, I have a complete original NES system for sale on eBay as well. It includes 2 controllers, 15 games, a light gun, and a Power Pad as well. You can find that auction here:
ebay: Original NES system w/15 games, Power Pad, Gun
Thanks for looking!