Anyone know of a range that goes out past 300 yards, that will accept new members, or take guests?

My current range goes out to 300 yards, and 9 times out of 10 that satisfies me. But I have a few rifles that I would like to stretch their legs, so to speak.

I know Greensburg and McDonald have 500 and 600 yd ranges, but I contacted both and they won't let me in.

If it means anything, I'm not looking for a range to regularly use... Maybe just 3 or 4 times a year, depending on how well I can shoot past 300.