If you’re going to access your local computer (or any computer) using UNC, you’ll need to setup a share. If you haven’t already setup a share, you could use the default administrative shares. Example:
\\localhost\c$\my_dir
… accesses a folder called “my_dir” via UNC on your C: drive. By default all the hard drives on your machine are shared with hidden shares like c$, d$, etc.