Check out Modular Paintball Gun Low-poly 3D model on CGTrader for $6. High-quality mesh by groundhog: 6400 polys. PBR, Textured.
STL (Stereolithography, filesize: 1.63 MB), OBJ (OBJ, filesize: 1.63 MB), TEXTURES (Textures, filesize: 46.2 MB), FBX (Autodesk FBX, filesize: 1.63 MB)