If I'm understanding this correctly, the Scourge system is a free update to the existing free-to-play game. The in game purchases I think are mostly sold from the in game shop, but the Epic Games Store listing shows some of what's available externally. Why this is different to the Steam version and, as far as I can tell, the console versions, I don't know. Maybe those are packs exclusive to the EGS version? Either way, all I can suggest is download the game and see what's on the game's store.