Well woodchuck could make any wood elements you need. I would saw adapt a flashgun for the barrel but it has an oval shape to it. I have seen replacement pistol grips for both real guns and paint guns (which the paint guns shouldn't be illegal?) You could use to mod for the gun grip especially as some actually have gaps for batteries and or chip sets for electric auto fire in that location. The top part of the pistol above the grip could be 3 d printed if someone designed it or once again woodchuck could help with it.
For the one part on the bottom it seems to have a shape simliair to metal rain gutters...maybe mod a piece to fit