And that would certainly be a mighty tome if all the tales of his vast library are correct!
I know someone who has quite a few books once owed by Tolkien, not to mention a lot that were owned by other members of the family. The trick is to look inside unassuming looking books and there will be inscriptions. I believe most end up in either antiquarian bookstores (such as Ulysses in London) or at book fairs, sometimes even in book dealers around Oxford. They aren't that hard to find, though the collectors
always know where to head and snap 'em up fast!