The frequencies for spirit entities are varied depending on the density, strength and type of the haunting. Spirits do not have individual standard frequencies because they move in and out of planes so rapidly the fequencies change each time. There is a base resonant frequency for each huating but to capture this may be very hard in deed. Studies are being done to try to nail at least some kind of base frequency to start from. Don't listen to these guys on HBO they do more to hurt this industry then help. Fraud is the word.
I think their at various frequencies. Not just one. Depends what ur looking for. Just think we all give off our own individual frequency. They say one day we will be able to comunicate thru telepathy. And to reach a specific person ud have to tune to their frequency. So I think it's like that. There are tons of frequencies with tons of things to comunicate with. Tool wise , I don't know. The only thing I know u can do is meditate and try an channel someone