An ESDV is commonly a block valve (e.g. a ball). Its not very comon to state theCv of a ball valve due to the high value. If its for simulation then usually the softeware will have some default. It will usually do.
My first choice would be to ask the vendor of the ESDV valve.
If they are for isolation, they are often gate or ball valves and a Cv may not be calculated for the data sheet. I've seen Cvs published for ball valve (Orbit valves, full and reduced ports have available Cvs) but as MortenA points out, they are often very large because the valves when wide open are low pressure drop items.
If you need an estimate and the vendor has no data, you can use the L/D values in Crane for gate, ball, etc. Using that and the friction factor you can calculate the K factor and then estimate the Cv using the approximate conversion factor in Crane.
