the U.S. Libertarian Party not extreme right, but are hidebound and doctrinaire about “free enterprise” system, including the aspects which don’t seem to be working well!. . . Or as far as more niche parties on the extreme right.
Anyway, U.S. LP pretty successful overall at getting ideas into mainstream of discourse and even policy, but then again, things a good chunk of people tend to believe in anyway. So, hard to know how much credit to give to tiny little party.
The Reform Party (starting with Ross Perot in ‘92) seems to have faded.
Other U.S. third parties are pipsqueak parties.