If you are looking for typical values, I'd get a copy of various vendor catalogues: Fisher, Valtek, Masoneillan so if you calculate you need a certain Cv, you can see what size of valve you need.
If it's a specific globe valve you have (eg. 3", class 600, Fisher ED, reduced equal percentage trim, etc), go to the vendor's website and see if they have the Cv information there or get a catalogue sent to you. If you have a serial number, the local rep will be able to get the information they have in their records for that valve.
