The supercharger unit itself is out of production, its my understanding Gruppe M has the capability to continue producing kits, but they no longer have access to the modified Eaton M90/Magnusson S90 that forms the core of the kit - the only way to purchase them now is used.
Several of the used kits are incomplete, or have been modified - typical pricing, when one comes up, is between $6500-8000 USD, I recently sold my Gruppe M (complete) for $6500. Most of the kits available are for 1991-1994 nsx's, I *believe*, based on posts here on nsxprime, there was also a kit produced for obd2 3.0L cars ('95, '96) but there was never a kit made for the 3.2L nsx's.