Step 1. Go to Steam.
Step 2. Right-click Garry's Mod and go to Properties, then go to Local Files.
Step 3. Click garrysmod, go to data, then move to adv_duplicator.
Step 4. Get any dupe you want from #gm-shared-dupes, download them and drag them into advdupe2.
Step 5. (optional) If you are in the game, click the Green refresh button on the top to show the New Dupes within the Folder.
If you have any issues, ask a GMV+, and they can help.
Place downloaded dupes a folder similiar to this: C:\Program Files (x86)\Steam\steamapps\common\GarrysMod\garrysmod\data\advdupe2