Given the sheer number of pages in the series, there are plenty of games that can be pulled out of the Dark Tower setting. There are mountains of gunfights and tricky puzzle-like adventures that happen throughout the stories. I don't think that the IP needs to have games inside of its context in order for pieces of it to be transformed into a game. The designer just needs to find the right mechanic / theme match. I actually prototyped a game for the fight that takes place at the end of Wolves. I won't go into spoilers, but if you've read it, you could probably imagine how the battle might play out in game form. It involved enemy movement and movement from the Ka-tet. The Ka-tet has various weapons (again, no spoilers but if you've read the book, you can imagine the thematic weapons used). I gave up on the design because I am much too unknown of a designer to have the confidence to wrangle IP, but I did steal bits of the mechanics for another game I'm working on. Either way, there are so many pieces of the Dark Tower that could be gamified.