A helicopter pilot experienced a NMAC with paragliders after sunset.

Narrative

During cruise NVG flight at 5;500 FT MSL experienced a near mid-air collision with a paraglider near a popular hang gliding/paragliding park. The time of the incident was 10 minutes after end of civil twilight and nearly 40 minutes after official sunset for that location. According to FAR these vehicles are only allowed to be operated between the hours of sunrise and sunset; so I was not expecting there to be activity at that time. As we contacted approach for our Bravo clearance; I noticed a paraglider high and to our 2 o'clock through my NVGs. While maneuvering to avoid this paraglider; I descended and maneuvered left at which point I saw a blue paraglider go beneath our aircraft by approximately 50 FT. No evasive action was taken because I did not see the glider until he was beneath the aircraft (seen through the chin bubble).Notified local law enforcement via flight center in the hopes that they could get a name of the offending paragliders and a report could be filed with the local FSDO. When police arrived; there were still a number of paragliders packing their chutes on the ground and none would admit to having been the offending gliders.