In the past I have used a product by the name of "cricket"
You simply wire this in to the valve (at the controller)you are looking for and activate the station.
It rapidly turns the solenoid on and off creating a lot of noise. You then walk the property listening for the ratcheting sound of the solenoid.
After finding the desired valve location simply remove
the cricket from the controller.
I know this may seem like it would not work....but trust
me it does and at about $20.00 it is well worth the money
good luck.