The Numbers Game chip is a custom. The only info on the die is "MC121".

Incredible Brain Buggy arrived: TMS1000NLL MP0915 MS^7923
It's simpler than Big Trak; up to 24 steps of forward, left, right or stop, each for 1/2 to 2 seconds.

There are quite a few TMS chips on ebay: MP0190, MP3301A (Big Trak!), MP1276, MP1185, MP0158 (Entex Soccer), MP1122, and more.