The 3rdpersonbuggy.zip file you have requested: Garry's Mod / Add-ons / Half-Life 2: Third Person Buggy View For Garry's Mod - 620.17kb is not available. Perhaps try browsing all files for the game Half-Life 2 and upload any files you want to share or are missing. This is the only information we could locate:
This allows you to view yourself driving the buggy in 3rd person view in Garry's mod. It's in mod form.