There is actually a book called Ferrington Guitars that was published in 1992 that features his custom made guitars and which you can pick up used at Amazon.
Ry Cooder owns 5 custom Ferringtons.
From what I've been able to tell just glancing around the net, Ferrington made unique custom built guitars for well known musicians.
The book, by the way, came with a CD, apparently audiophile quality sound, and apparently with a lot of name musicians playing custom Ferringtons.
My impression is that he is a highly regarded luthier.
I don't understand the relationship with Kramer. There is a Ferrington on Ebay right now. Read the
description. This particular guitar isn't labled Kramer, just Ferrington, but apparently was a production run while he was at Kramer. And the description says there were four such production runs based on guitars that had previously been custom builds for specific clients.
If it were me, I would spend the rest of the day doing research on the web. But based on my initial reading, if it's a custom built Ferrington it might be a pretty special instrument.