AntiMicro is a fantastic gem of an application that allows you to map keyboard and mouse input to a game pad. I used this to play a game called Pokémon Insurgence on Lutris that had no Gamepad / controller support. AntiMicro and allows you to map Keyboard and Mouse Controls to Gamepad. It’s probably on all Linux distributions or at least should be.
Are there other options? Have you run into such issues playing older DOS based games?