I haven't seen a dealer yet who has a bike in good condition. I purchased mine from a garage/dealer who obviously pieced it together but tried to sell it as an original SP. However, since he had it apart he cleaned most of it up for me but I paid a bundle for it (approx $5000 usd).
The only chance you have is to find a dealer who is also a personal collector. These bikes will usually be in good condition. The rest have been thrashed on the road or stored outside in humid weather which means lots of rust and corrosion.
I know one dealer who is thinking about selling one of his bikes from his personal collection (he owns 1 of every NSR built). I'm sure if you offerred him enough money you could get it. I think it is a Rothmans SP (original everything + low km) and he wants $7500 - $8000 USD for it.