If you're using a TTF font you can see what's available (and the ASCII number) you can use Windows' built-in Character Map (in Win10 it's under Windows Accessories); if you're using an SHX font download the Character Map AEC file from DC LLC (
https://www.datacad.com/ddn/fonts_ref.html - links to PDF and AEC files are under "DataCAD Standard Font Chart") and change the font to the one you want to use. If it's not shown it's not available.