You know about Claybank, plus I have secured and used no less then 8-9 other places for Airsoft, and Paintball (long and short term)
I always use the direct approach to finding what I need. I find the location first, then I go after the owner for permission. You have to be very good, and fast at reading people. You have a very short time to make a good impression, and it better be the right one, or they will say no.
Sometimes when you do get a "no" it's for a good reason, even though it doesn't seem that way at the time. This happened to me a few times when I was opening one of my fields, but the location I ultimately secured was much better then the first ones anyway...so it worked out very well.
Operation Mason Relic Owner