When you go into the character screen to upgrade a specific weapon, you can hover over where it says "upgrade materials" in order to find out how to get the materials required to upgrade that weapon. When I hover over it, it says that "weapon parts" can be acquired from the Gunsmith or from dismantling weapons. I have, of course, gotten them from dismantling weapons, but every time I go to the Gunsmith that is up behind the Cryptarch, I don't see an option to buy them or acquire them in any way. Does anybody know how to get them from the Gunsmith? I'm to a point where I don't have enough weapon parts right now to upgrade my weapons just from dismantling weapons alone, and I wouldn't mind supplementing it with buying some from the Gunsmith. Unfortunately, I can't figure out how to get them from the Gunsmith. Any help would be appreciated.