Hi Lowell and welcome to Prime!
If you want to use a specialist, they are becoming fewer and fewer every year as many of the original factory-trained techs (the ones Honda flew to Japan for training at the actual Tochigi factory) are retired or retiring. Ben at Daisy Auto is probably the closest to Charlottesville, but it's going to be a drive.
If you have a 91, then you're going to need more than the basic TB/WP service, which is what a specialist will tell you. The engine is now more than 30 years old, so even though it is a Honda, it still needs maintenance because all of the rubber seals in the engine are way past their designed service life. In the NSX world, we call it the "engine refresh," which is based on what Honda does at the NSX Refresh Program in Tochigi. You've got two pathways: you could do the "stage 1" engine refresh, which does not remove the heads, but replaces all of the accessible rubber seals on the engine. It's about $500-ish in extra parts and labor because you remove the cams. Or, you can do the "stage 2", where you remove the heads and replace the head gaskets, along with the oil supply port seals in the block. This is partially dependent on whether your NSX is leaking oil past the valve seals and your exhaust guides. Both of these parts tend to drift out of spec around 100,000 miles. The valve seals go sooner because they are made of rubber. They won't really affect performance, but you may get puffs of blue smoke under hard throttle. As for the head gaskets, it's more a function of miles and usage than age, but we're starting to see more failures in the sense of weeping leaks (versus complete blowouts, which are rare). Thus, many owners choose to replace them to ensure 30 more years of reliable running.
So, no matter who you take it to, make sure to mention this. If the engine is coming apart for the TB, it's crazy not to save the labor and do the rest while he's in there.
Hope this helps.