As you've said, the lore has it that Graff originates from the Dark Tower series. Hence, the name Graff, which was said to be a light, refreshing, apple-based beer. IIRC there's even something about maltiness, which led to the 'creation' of the style.
However, you're looking for something older than the series. For this, we need to find a recipe of an apple beer, brewed or published prior to June 10th, 1982 - the publish date for The Gunslinger.
A quick-ish search of the Google-ator doesn't reveal much, however there are a few things that we can determine:
-Graf (or graff) is a fruit beer.
-Fruit beers have been around 7000BC
-While rare-ish, Pomme isn't an unknown lambic ingredient. Lindemann's makes one, but they first made it commercially in 2005.
This sounds like it would be a fun project to do more intensive research on. The conclusion that I'm led to, based on what's available to me at the moment is that, while it existed a priori, I find no evidence of commercial variants prior to the last 10 years.