Brian,
Since it would be of no use to you to go directly to the Masonic temple itself, my advice would be for you to go into the police station or city hall, (not call) and approach an officer there. More then likely one or more of the policemen in your city or town is a Mason. If you know an officer that would save you a step. He in turn can put you in touch with or speak for you to the "Worshipful Master" of that lodge. That person is the ONLY one that can grant you permission to detect that property. My guess if you explain what you want to do, how you will do it, and the condition you will leave the property in, you will have no problem getting WRITTEN permission to detect. It would also behoove you to assure him you would return anything you find Masonic back to the lodge. If the answer is no it may well be someone messed it up for you by not gaining permission beforehand. Thanks in advance for doing it right........Gil