Calipers to measure then draw a diagram with the measurements.Someone could then do a model in a 3D program. Saved as an STL format then it is turned into G-Code for 3D printing.PETG would probably be the filament of choice as it is some of the strongest. Infill and walls would need to be addressed to handle the pressures of air and movement through the breach area.I had a couple SMG .22's at one time so I kind of understand what would be needed.
Possibly a starting pointhttps://www.thingiverse.com/thing:4763897Dave