I recently went through my own search for a gym that allows independent trainers to rent space. Karin and LaRue both have it right that smaller facilities are your best bet.
I just searched for gyms in my area and emailed/called each one asking if they allow independent trainers there. A couple got back to me and I met with their fitness directors to check out their facilities and discuss what type of agreements would be fair. I ended up finding one that had everything I needed and an agreement that I felt was fair.