Hi Runedog
You mention regular music is too small for you. Have you checked out any of the many EZ play books by Hal Leonard? The notes are huge and even have the letter names written in them.
Otherwise, I believe anyone can learn how to play by ear if they know what some might call the secret.
The simple answer is, is if you can sing it or hear it in your head, your fingers will go to those notes, IF, you do not interupt your thinking with things like, what is the next key, what fingering should I use, etc, etc. That will throw the monkey wrench in this and people think they can't play be ear.
If a person learns at least the most important chords, at least, like the 3 primary chords, the secondary chords and something of their relationship and maybe even a few scales, then if you know that almost all songs start on the I chord and that the melody notes almost always start on the 1st, 3rd or 5th of that chord, giving you a starting point, and if you go with that, even if by trial and error, and then playing along singing or hearing the melody in your head and listenting to when it sounds like you need to change to a different chord and then realizing most of the time the melody note will fit one or two of the main chords and testing it out on the fly, then anyone will be able to play by ear. As long as they remember how the song goes

If anyone has an interest in this or other things related to playing keyboard, piano or organ, I am currently teaching long distance by phone, and am starting a student probably next week using a webcam.
Best
Scott
http://www.ScottLMusic.com