Hi & welcome.
Plans in Surrey have one for sale that might be a good place to start your search:
http://www.nsxuk.com/#/1991-manual-coupe-formula-red/
Just had a look at what is available on the big Japanese car sales sites - asking prices range from GBP 27,500 for a 1990, to well more than double that for a low mileage '91. Most are 1991 models - manual cars made 1992-96 are very few and far between at the moment.
Sorry can't help more than this.
Good luck with the search.