The information provided is insufficient to identify your gun. The Highland Arms name has been used by several firms, past and present.
The best way to determine what you have is to post some photos of the gun. Remove the forearm and separate the barrels from the frame. Then take some clear, close-up photos of the top, sides and bottom of the frame and the breech end of the barrels and all markings that appear on the barrel flats and frame watertable. A photo of the assembled gun would also be helpful.
A maker, importer or distributor name and city should be stamped on the gun. In the case of an import, maybe the maker
and an importer/distributor. If the gun is an import, the proof marks will tell us a lot.
Let's see some pix!
DF
Montani Semper Liberi