You need to get a form ATF 6 or 6A and then find an importer. I am told you can do this on your own but when I looked at the form on the ATF website I didn't know how to fill in half the stuff.
The easy way is to contact an importer who will do the paperwork for you on firm is:Leroys Big Valley Gun Works
200 1st Avenue North
Glasgow, Montana USA 59230
Telephone: 406-228-4867
Contact Denise Tiffany

It takes forever, but it happens eventually.

Great-Great Grandson of D.M. Lefever
www.lefevercollectors.com