There are a number of places out there (I used a rolling road at Sigma Engineering in Gillingham, Dorset) but whoever you use, make sure they have knowledge of your induction system. If you have a holley carb make sure they know holley's and have the spare jets etc to hand. If injection make sure they understand injection etc etc. You don't want to waste time on an expensive dyno. Sigma were good with Holley's.
Malcolm