For players of games like War Thunder , custom "skins" are often packaged in zip files:

TM 9 7218 M 42 Duster Twin 40mm : US Army - Internet Archive

: Provides historical camouflage skins like the M42 Duster of the 4-60th , used during the Vietnam War. Historical and Technical Documents

: This search engine lists various 3D models from across the web, including free and paid files. Gaming Skins and Mods