New craft weapons: keep researching looted personal arms and related topics, you will get there (in 4 or 5 steps). There's a ton of them. If you can't, it could be related to the tech tree troubles, 0.76 should fix most of these. Lootable vessel weapons are possible to implement, but you'll have to wait, it'd require major rebalancing - I want to finish the current "to do" list first.
30mm cannon: It's unavailable as in: you can't get more of them until you research it, but you happen to have a single weapon of that type in stock, presumably stolen from somewhere, and ammo is commonplace enough to be buyable (even if the price is high).
Advanced Firearms: it's kind of an empty topic for now, but this will change. There will be several very good weapons (for firearms) available there.
Maunufacturable weapons: nah, generally only completely new weapons are supposed to be manufacturable, the rest has to be looted. I want the player to be forced to improvise a bit with weapons loadouts.