Originally you could only get the weapon from Sebastian, however it wasn't supposed to be a unique item. Since there's a schematic art for it in the game, it's plausible that there was supposed to be a schematic for it but Troika just forgot about it. I had to come up with the schematic description myself. The schematic can be bought from quality smiths (5% chance).
Schreck's-Multi Barreled Pistol:
Originally, the schematic for this weapon (in Bates' factory) was made unusable intentionally, so the weapon was cut out for some reason. The graphics for the schematic and the weapon itself are in the game, however the weapon had obviously wrong stats (D:1-6 FT:1-3 RNG:10 Speed:15 Bullet:1), I changed it to D:1-20 FT:1-5 RNG:10 Speed:15 Bullet:6.
There are schematics for Clockwork Physician, Illuminated Decoy and Explosive decoy in the game . There are items as well, but no actual critters or scripts. They most likely got cut out due to the time constraints. But they are now finally finished. The art for decoys' critters already had other palettes and I decided to use them for the restored decoys, so this way Clockwork Physician is green, Illuminated Decoy is yellow and Explosive Decoy is red. I also made new inventory art for the decoys' items, that reflects these colors. Here's how the decoys function. A Clockwork Physician follows you and heals you just like a Medical Arachnid, it can't attack anybody (and doesn't provoke anybody, unlike the original Clockwork Decoy). An Illuminated Decoy follows you as well, it carries a large light, never attacks and never provokes combat. An Explosive Decoy acts just like the original Clockwork Decoy, but it explodes when it dies, hitting everybody with 5-30 of normal and fire damage in a radius of 2 tiles (just like Explosive Grenade that is used to make it). I tried my best to follow the schematics' descriptions, so I believe these were the original intents. All three schematics can be bought from inventors (10% chance).
Levered Machine Gun:
This weapon was probably supposed to be a unique item, since there's no trace of a schematic for it. Although the graphics for this gun were finished, the stats were obvious placeholders (D:1-15 FT:1-3 RNG:15 Speed:15 Bullet:1), I changed them to D:1-40 FT:1-5 RNG:15 Speed:20 Bullet 6. The only copy of this weapon is now given to Captain Wheeler.