The thickness may be a problem; nonetheless, try:

1) Polishing Corp. of America
430 Martin Ave.
Santa Clara, CA  800-672-0060  408-988-6000
sbpca@aol.com
[fast turnaround; quality has not met our standards]
2) Okmetic, Ltd., Espoo, Finland
358-0-502-800
3) Semiconductor Processing Co.
12 Channel St. Suite 702
Boston, MA  02210
617-345-9936
--
Albert K. Henning, Ph.D.    415/617-0854 (Office)
Redwood Microsystems        415/326-9217 (FAX)
1020 Hamilton Avenue        henning@redwoodmicro.com
Menlo Park, CA  94025       http://www.redwoodmicro.com