If you will opt to stick your mirror on your windshield, please do avoid using the local superglues such as Mighty Bond, etc. (no offense on these products). My friend had an experience with these and resulted in the breakage of his windshield. I guess the chemical properties of the superglue had a bad effect on the windshield.
Have you tried the different surplus shops that sell parts? Parang malabo na mahirap hanapin. Try contacting Saulo or Tango since they have lots of surplus items