I went to a dental supply business and asked for a box of front surfaced dental mirrors. They are mounted in a stainless steel mount with a short threaded shaft on them which can be cut off or retained depending on your application.
I also perfected a method of extracting the mirrors from the mounts. It involves filing a groove through the edge of the mount right through to the glass at intervals, a little over half way around the circumference. The sections between the grooves can be folded out using needle nosed pliers, releasing the mirror.