You can always make a huge list using Combine validators e.g. a Combine-AND: "Player supply available"+"Target unit compare field: supply" for every supply number in the game, then stuff them all in a Combine-OR to use as the main validator. Don't forget the case "supply>=0" which should go directly in the Combine-OR bracket to allow controlling supply-neutral and supply-generating units.
You can always make a huge list using Combine validators e.g. a Combine-AND: "Player supply available"+"Target unit compare field: supply" for every supply number in the game, then stuff them all in a Combine-OR to use as the main validator. Don't forget the case "supply>=0" which should go directly in the Combine-OR bracket to allow controlling supply-neutral and supply-generating units.