I don't know what changed exactly, but the caliper parts on the Edge changed in 2010/2011. I think they added an engine or trim option, so there might be multiple part numbers for the edge. The CX-9 part numbers are consistent from 2007-2015. It appears that one of the 2011+ Edge caliper part numbers would probably work on the CX-9.
I've bought a lot of stuff from Rock Auto, but I've never done a core exchange there. Shipping auto parts gets really expensive fast - they are heavy and UPS/FedEx charges mere mortals like you and I a lot for heavy items. I once sold a set of coilovers to someone on a forum, and the shipping was somewhere near $100 because of the weight.
Amazon sells auto parts now - I'd check there if you were trying to get something cheap. If you have Prime, they will ship the parts for nothing, which can be a big money saver. Their prices are usually close to Rock Auto, but the free shipping can tip it in Amazon's favor.