There is the Reichsbürgerbewegung which pretends that Germany still exists in the borders of the Second Reich; as such they first appeared after East Germany was annexed by West Germany but they naturally had predecessors on the radical right of both countries. In Austria and West Germany you have monarchist student fratenities (Studierendenverbindungen) which were not banned because they also were prosecuted under the nazis (who attempted to fuse all fraternities with the nationalist Burschenschaft Germani)a. In East Germany all the conservative fraternities were banned but they were reinstated shortly after the unification which suggests they did exist to a degree in the underground.

The Rightwing organisations in the underground are a touchy subject. The German press will now and then reveal East German state security (StaSi) created it's own illegal rightwing networks to have all the potential activists in touch. However it was recently revealed the West German state security (BfV) was doing the same and the most ugly part of the story is their agents were apparently in touch with groups murdering foreigners without reporting any of this to the police or to the public.