Depending on how you feel about "foreign" parts...
I was doing some looking for winter wheels and in my searching discovered that the chrome clad 18" wheels used on the Ford Edge have the same bolt pattern diameter and are the same width. If the center hole is the same size (and i suspect it may be) then those wheels would likely fit the CX-9.
They do look very similar to the standard Mazda wheel. Will they absolutely fit? I can't say for sure but the important dimensions are identical, the Edge and CX-9 share the same basic platform, and there are plenty of FoMoCo labeled suspension parts hiding underneath the 9 - I've seen them. The only dimension I haven't been able to find on these wheels is the offset.
Chances are really good the Ford wheels will fit and the center wheel caps may even be interchangable too. It might be worth a look. You may even be able to find a takeoff set of these for a good price.
Ted