It depends on whether you are already a Medicare beneficiary. If applying for the first time, you can reach the Social Security Administration at ssa.gov/pgm/medicare.htm. There is a button which activates the application for first time enrollees.
If you are looking for a replacement card, go to sss.gov. Call the phone number listed on this site.
If you are looking for a replacement card, go to sss.gov. Call the phone number listed on this site.