This is quite old by now but if your looking into getting a Intellivision you may want to consider looking for one of these. I’m not sure if they sell them anymore but you can find them usually on eBay for next to nothing.

The controller comes with 25 games build and all you need to do is put in some batterys, plug the controller to your tv and soon you’ll be playing classic games such as Astrosmash, Space Battle, Buzz Bombers and many more favorites.