1. Personal opinion: the recent Greyhawk novels are not worth the read. I recommend the Gord novels by Gygax, Nightwatch (by Robin Bailey), and Quag Keep (a proto-Greyhawk novel by Andre Norton). Avoid anything by Rose Estes like the plague. All of these are long out of print but used bookstores may have copies.
2. Lots, but most are out of print. Much of the Carl Sargent stuff is pretty good.
3. Check the WotC website, they used to have quite a bit available. PDFs of out of print stuff are available from a company whose name I can't recall - google for out of print tsr products. Also check the Greyhawk webring for stuff others have written.
-Phil