Not on GOG itself, but in
Impulse, they've got Total Annihilation + Core Contingency for 10 bucks, fixed up to run on modern Windows. Definitely a Great Old Game. My all-time favorite.
Some of the greatness of this game was in the replayer, which let you watch your games later, or watch others for fun or instruction. That was as fun as any movie you'd see in the theater IMO and a tremendous instructional tool. I miss it mightily in any game that does not have it. But I think that was a third-party add-on. I wonder if it works with this version.