I googled the Yamaha guitalele, found a photo or two, and it looks very likely. The problem is that almost all the web sites were in French, Spanish, German, or languages that I didn't recognize. I found one web site in English, but I couldn't tell what country it was. It had an "en" prefix before the body of the URL. England? I've visited a lot of English web sites, but I haven't seen that before. Anyway, the Yamaha guitalele on that site sells for 60 Euros.
I found one on eBay and one on Yahoo auction—both sold. I did learn that it's tuned like a guitar with a capo on the fifth fret (like an "alto guitar"), but nothing about replacement strings. And the interesting thing is that I went to the Yamaha web site and they don't even acknowledge its existence.
It looks very much like what I want. But being in the U. S. of A., where could I find out more information about it, and where could I buy such a thing?
I can't find anything at all on the Johnson hybrid.