The Anglo-Saxon riddleworld
Cynewulf and the Exeter book
Riddles in the dark
The riddles of the all-wise
The puzzle of the two hobbits
The riddle of Bilbo's pocket
The riddle of the ring
The Lord of the rings and the riddle of writing
The Volsung riddle: character in Tolkien
The enigma of genre fantasy
... And back again.
OBNB doesn't sell books, but you may be able to find a copy at one of these websites:
The Riddles of the Hobbit by Adam Roberts. ISBN 9781137373632. Published by Palgrave Macmillan in 2013. Publication and catalogue information, links to buy online and reader comments.
