I don't think you can do a private sale under CA law, but you can check. If not, the only way to legally sell it would be to a dealer and I doubt very much any dealer will take it, even in trade. Since those guns were made throughout the late 19th and early 20th centuries, yours might or might not be an antique (pre-1899) under federal law.
The trouble is that those guns have little or no collector interest (though the English-made guns do), and are valued at less than $100 even in top condition. Since they are old and of little value, dealers don't consider them worth the paperwork required to buy or sell them.
You might consider using it as a decorator/wall hanger of some kind. In some decor, an old gun in a shadow box makes a nice addition.
Jim