Does anyone know how I would go about asking an author if I can use a novel of his as source material for RPG rules? Agent? Lawyer?

You can write to the author's agent. You can find most author's contact info on the internet these days. Otherwise, contact info is often on the jacket of an authors hardback book.

If you can't find it with these sources, you can email the publisher or write to the publisher.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.