Somewhat hard to find used although they do come up on Fleabay or the IBMWR Marketplace occasionally.
To my knowledge you can no longer buy a set new. However a couple of years ago I bought a new pair by purchasing the right and left separately. It took a while to get them because they had to come from the fatherland. You'd need to order a left case (part 46542316595), a right case (part 46542316596) and a set of four lock cores w/key. (part 46542315023) Not sure if you can still order the lock cores but I know that you can get a set of six lock cores with key (part 51252303683) because I bought a set of them last week.
This is from a set that I picked up one at a time on Fleabay and then had Line-X'd to match the other Line-X on my K1100RS. See the photo at the top of the page to see what they look like when mounted. They use the same mounting "Z" racks as the full-sized integral cases.
(http://i1221.photobucket.com/albums/dd470/Motobrick/luggage/citycase_closed.jpg)
(http://i1221.photobucket.com/albums/dd470/Motobrick/luggage/citycase_open.jpg)
At about $20/bottle, the Mondavi Napa Merlot is an excellent buy. Be sure to get the Napa Valley stuff though, not their run-of-the-mill merlot.