I still play it fairly often actually. I enjoy it though I will agree it is a terrible game. But I think that's part of what makes it enjoyable to me. So no judgement from me if you want it haha. Plus you get to feel like such an awesome lone Firewarrior taking on space marines by yourself!
I'm actually stuck on the level where you enter the warp... the chaos space marines all have some sort of rocket launchers that make it near impossible to hide from them, and the rail rifle takes 2 head shots to kill them -_- . And ammo is way too limited lol.
And amazon and ebay are pretty much the only suggestion I can make for your problem as well.