Weapons can only be bought from Gryph (his location is marked on the map), but they'll always cost you an arm and a leg. Now, the good news is that it is possible to receive weapons in several quests throughout the game. The bad news is that you usually have to pick a particular conversation option to get them, and it's not always obvious which one. As a rule, if someone mentions guns and you can continue on the same topic, do so. There's also a game guide, if you feel like playing *like that* (I did, but it's probably not the best way to appreciate the game).
The clothes are a bit easier to get, but the good stuff only appears in stores during the last few days, and they're pricey as well. You'll be able to... come across them in other ways if you're lucky, though. I'm not sure how much you know about the game so I'm trying not to spoil it
Not sure I know what things with domed heads are you referring to, probably the "worms"? They're steppe creatures, you'll find out bits of information about them from dialogues if you pay attention (as with everything in the game).