You should submit AC Form 8060-56 (PDF) to:
Aerospace Medical Certification Division, AAM-331
ATTN: Duplicate Desk
PO Box 26200
Oklahoma City, Oklahoma 73125
You must include a check or money order for $2.00 made payable to the FAA. The Aerospace Medical Certification Division can fax you a record of your certificate that is valid for no more than 60 days, which should be enough time to receive your replacement certificate. To receive this fax and order a duplicate certificate, call (405) 954-7674 to reach the duplicate certificate desk.
Page Last Modified: 04/16/13 07:59 EDT
This page can be viewed online at: http://www.faa.gov/licenses_certificates/medical_certification/faq/response17/