Tracy-

You can try the MEMS group at Case Western Reserve U. in
Cleveland.  They have done some real nice CMP research
(polishing polysilicon, oxide, silicon carbide, etc.),
but I don't know if they offer that service.  The contact
there is Jeff Melzak.  He is the Microfabrication Lab (the
fab cleanroom) manager, but he handles all outside inquires
for all the MEMS facilities.  His phone number is 216-368-3628
and his email is jeff@mems4.cwru.edu.  You can tell him that
I suggested you call him, I had used their CMP systems when
I was a grad student there.  You can also try the Polishing Corporation
of America (PCA).  They can be reached at 1-888-8-WAFERS.  I have
not gotten any CMP done by them, but I know that they offer CMP as
a service.

Good luck.

-Kevin