Hey! At the moment I'm working on adding all the maps from the main campaign into Gamemaster Mode. It's far from complete, there's some maps I can't convert without crashing (like Reaper's Coast, unfortunately), but there's a lot that can be done with what's included so far! Steam version can be found
here, there's nothing for GoG users currently but I'll get around to working something out. Have at it, if you find any bugs (especially any crashes to desktop on the Fort Joy map) list them out here and I'll work on it as soon as I can.