Apparently, I do mean "Video Game Brain" but a homemade device that gives you two cart slots and allows setting A12 high or low on either slot would also work.
It would be easy to lay out a board for such a device, and would not require any logic chips. The edge connectors (either through hole, but deep enough to insert a cart, or straddle-mount) might be hard to find for a reasonable price, though.
I'm trying to find information about the "Video Game Brain" but i also just keep pulling up the unreleased Game Brain. Do you think you can link me to the relevant information about it. I just cant seem to find it using Google.