DoubleBarrel OverUnder :
https://sketchfab.com/3d-models/stoeger-condor-outback-ou-shotgun-6f083a5d1c7d4fdebefb5daa8ac5af15

Lever Action 1887 SG
https://sketchfab.com/3d-models/winchester-model-1887-eb83af210c194cd7a30e2e2883977f79

Trench GUN 1897 :
Model got removed from sketchfab :(

Browning AUTO 5 :
Gmod workshop

shorty compact Shotgun :
https://sketchfab.com/3d-models/remington-870-with-magpul-furniture-07d1fce010ef4127931e8ddd516713f8
https://sketchfab.com/3d-models/shorty-shotgun-c61c79e8cbad43eaa1be6eed70073b64
https://sketchfab.com/3d-models/benelli-m4-7f88ac8b30084142b74443bfd173b33d

SPAS 12
https://sketchfab.com/3d-models/spas-12-shotgun-a0f118ec8a984f09b602fb3a54f56a9e
https://sketchfab.com/3d-models/spas-shotgun-fea7b12a18d24b8da18d8019f82496b9
https://sketchfab.com/3d-models/spas-12-1a83677b59a047878eebd29199926707

M1014
https://steamcommunity.com/sharedfiles/filedetails/?id=2993838423

and many others for additional parts