Instructions
Download the WireMod add-on for GMod and double-click the file to extract the content.
Open your GMod installation directory and place all the WireMod files into your Add-ons folder.
Double click the file "wire_download.bat" to begin installing and wait for it to complete. The Advanced Dupe tool is installed with the WireMod.
Close the file and load GMod and open the creation menu. Scroll down the tools list and select the "Advanced Duplicator" tool.