I'd have to look at the flyers again to make sure, but you could order the upgrade cards for your Turbo to play Duo games. Surprisingly, Radio Shack could order the games as well.

I'm oddly not shocked, Radio Shack used to be huge. What's more surprising is that they didn't use the Tandy name on a Turboduo, then try to sell it. After all the VIS was a great success!