The file 'Airbrush Handle For Brandless/generic (smoothed) 3D Printer Model' is (stl) file type, size is 145.5KB.
made the grip's back smooth and rounded off the top mount hole
hint: if the top does not quite slip onto your airbrush just take a flush cutter or something else to split the layers so you're left with two half-circles, so the halfs snuggly fit your airbrush… I know this sounds janky, but pre-splitting and supporting it during print is annoying and there are so many different diameters out there (all withing more or less a mm, but still …) that yours might just fit without cutting, who knows.
Mine didn't and I am perfectly fine with the post-split grip.
EDIT: added a picture where to cut in case my terrible instructions where not understandable 😬
airbrush_handle_generic_brand_smoothed.stl | 301.8KB |