The DLC for this game can only be bought via Steam or as a part of the collector's edition from the website. Because of this, the DLC is not officially sold on Linux, but it can be used with the Linux version after being bought on Steam.
for x in `find . -name "*.dds"`; do convert $x `dirname $x`/`basename $x .dds`.png; done
Upon install from steam on Windows 10 if you get the error "Failed to initialise 3D Engine," go into the user profile's Documents folder then My Games and delete the GratuitousSpaceBattles folder. Then relaunch the game.