Is there a resource yet for when and where the different authors will be having book signings?

Yes, the event catalog.

I only found Salvatore and Hickman in the catalog. I've never been to GenCon before. Is it possible that an author or artist might be just sitting in a booth somewhere and might sign their work? e.g., Elmore, Easley, Caldwell, etc. Also, if this is a thing at GenCon, do they typically ask for a fee to sign, like celebrities at other conventions sometimes do?

Chris Jackson offered to sign two of his books for me.  He was just sitting in a booth.

Margaret Weis, Larry Elmore, and Wayne Allen Reynolds have been more than happy to sign books for me at their booths. None of them even remotely asked for a fee. 

I bought the Eye of the Beholder film at Larry Elmore's booth one year and he was willing to sign it, over a piece of his art on the cover of course.

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