Goto Steam > steamapps > common > GarrysMod > garrysmod > data > advdupe 2; you will see the names of all your dupes, make a copy of them > Reinstall steam > Goto the same folder and repaste them.

Goto Steam > steamapps > common > GarrysMod > garrysmod > data > advdupe 2; you will see the names of all your dupes, make a copy of them > Reinstall steam > Goto the same folder and repaste them.