Drop Dragonlady a PM - they're up your way. See who they use for servicing.
Otherwise, I think VTECDirect are in Cheshire (depending on which side of D'shire you live)...they do NSX work.
Other thought in the N-West are TDi North (Warrington, I think) - they've got a good rep with most other fast-Honda owners, not sure if they do much NSX work or not...
If you want to stick to main-dealers, then there's no official list anymore, and the trained techs could have moved anywhere, so best going somewhere either (a) you've already got a good relationship with; or (b) that work on other NSXs already.
"No man with a good car needs to be justified"
Blue '08 FD2 CTR - big, ITR-sized shoes to fill...
Yellow '96 NSX 3.0 - oh was it worth the wait!
Black '99 ITR - well, I had to have another one, the first was so much fun. Miss this one even more than #1...
Blue '03 S2000 - SOLD, flawed but fun
Blue '04 Focus TDCi Sport - SOLD, very good fun for a diesel!
Black '00 ITR - SOLD, still missed
Red '98 Civic VTi - SOLD, probably still bombproof