FTL reminds me off PSI5 Trading Company on the C64, my first game I ever bought

I only made a mistake not to buy it on the developers homepage, but to buy it on steam. Buying via the homepage gives me the steam-key and the standalone-version of the game even for linux. Is there a way for steam-"buyers" to get the standalone-version (win and linux), without buying the game onece again on the developers hp ?