I'll need some good quality first surface mirrors for this to work.  

The angle of incidence of the small first mirror (24 degrees currently) is high enough that the thickness of glass I would have in a regular mirror would generate significant double images otherwise.

So far the likely DIY candidates are:

• painstakingly wet sanded and polished stainless steel.
• removing the protective coating from the back of a regular glass mirror exposing the silver.

Wet sanding the stainless actually worked, mostly.  The problem with this approach I found was I could flex the stainless enough to distort the image just by pressing on it.  This doesn't lend itself to generating a perfectly flat surface.  Once my first try was done, I found I had generated a concave mirror with a focal length of about 6 feet just from the pressure of my finger on the center of it while sanding.  

I suppose the next step would be to temporarily mount the stainless to something that won't flex like a block of aluminum, and then repeating the sanding.

For the second idea I'm still waiting on the coating to dissolve.  Acetone seemed to soften it, so I've put the whole mirror in a cup of it and I'm waiting.  I'm hoping that whatever was used to silver the mirror won't also dissolve once the coating is removed.  I guess we'll find out tomorrow.