I've got a project that would be ideal for use with electromechanical display technology, similar to what you see on transit buses or in airport/train station signs. These displays come in either 7 segment or matrix varieties. They are typically yellow and very high contrast for very good daylight viewing.

I've been able to find a source for new displays, but expensive. Considering these types of displays have somewhat fallen out of favor (maintenance?), I figured I could find some used displays fairly easily, but have been unable to find anything used or surplus. Any ideas?

On a related note, I've seen some 7+ segment displays at rental car counter signs that look to be standard LED displays, but they are super high contrast. Any idea what these are or where I can find a source?