> I had been looking for the now almost rare 3X5 version

Yes - I think the only currently manufactured 3"x5" glass signal mirror with a retroreflective mesh aimer is the US military issue 3"x5" glass MIL-M-18371E Mark 3 Type II signal mirror manufactured for the US Forces by S.I. Howard Glass.

Thankfully, the MIL-M-18371E Mark 3 Type II is available from several retailers online - just search for MIL-M-18371E.

One option is John D. McCann's Survival Resources: http://www.survivalresources.com/Products/Signaling.html

John had a nice article on retroreflective aimer signal mirrors that seems to have been lost on the current Web, but can be viewed here at the Internet Archive: John McCann: Signal Mirrors Can Get You Rescued

John's book: Stay Alive! Survival Skills You Need devotes at least 5 pages to signal mirrors.

The 2"x3" glass MIL-M-18371E Mark 3 Type II is available at a number of retailers as well.

Background:

The available selection of currently manufactured retroreflective mesh signal mirrors has been roughly halved in recent years with the deaths of Malcolm Murray of Rescue Reflectors (something like six models gone), and Wayne Tegeler of Vector I (who made 3"x5" and 4"x5" glass models as well as the 2"x3" glass and a 2"x3" plastic encased glass mirror - the 2"x3"sizes are still available from Coghlan's, who bought the business after his death. Another victim of this is that the my favorite 2"x3" polycarbonate signal mirror, the original retroreflective mesh aimer Rescue Flash designed by Doug Ritter and sold by American Medical Kits is no longer manufactured with the mesh aimer ( Wayne Tegeler had been willing to supply the mesh to them, but it seems Coghlan's was not willing do do so), but now uses a perforated retroreflective fabric aimer.