The ones that comes to mind for me Silver Legion of America and the Silver Legion of America.

German American Bund Founded in 1936 was an organisation filled with Americans that came from German immigrants.Lead by Fritz Julius Kuhn their role was to promote friendship between and show Nazi Germany in a favourable light. They also ran camps for kids around the country and held in a rally in Madison Square Garden. The organisation was dissolved in 1941 after the US was declared war on by Nazi Germany.

Silver Legion of America Was more of a purely pro fascist political party. In fact William Dudley Pelley the leader of the legion ran for president in 1936. . Again they were shut down when the war broke out.

Fritz Julius Kuhn and William Dudley Pelley were both arrested and imprisoned. Kuhn got deported and died in Germany whilst Pelley died in the US.

Source:United States Holocaust Memorial Museum