GQ11 is an "official" set of 12 tiles that was inserted in the Games Quarterly magazine (issue #11) and published by Rio Grande Games. You can buy the magazine (and the tiles) online. The site I use is
Funagain, but I would strongly suggest you shop around to get the best price for you.
If your local game store carries the German edition of "Graf, König und Konsorten", I would suggest that you get that instead of Rivers II, as the German edition also contains a copy of Rivers 2 as well as a previously published expansion, Count of Carcassonne (Graf), the carcassonne half of the King and Scout expansion (König), and 5 shrine tiles (also published separately as Shrines and Heretics as a magazine insert - in a German magazine, but you can also get those 5 tiles in Cult, Shrines and Creativity published by Rio Grande Games). The advantage of the german edition is that the tiles have a "watermark" on them so as to allow you to be able to sort your tiles by expansion easily.
Also, before you purchase your copies of I&C and T&B, you might want to ask if there are watermarks on those expansions as well (which will help you sort them out after the game).
Urgh, sorry, I'm babbling... but if you do have any further questions, please do feel free to ask here