I think you have to buy through distribution but I've only dealt with them for datasheets and quotations on a past potential project. You might search eBay to see if anyone is selling their used ones.
These are what I call a raw panel which means the input is a LVDS signal so you can't directly connect a composite video signal. The board that I referred to will accept a video input (anything from HDMI down to composite (RCA Jack)) depending on which board you purchase.
There are 2 companies that I can recommend for the interface board. I buy direct but they also sell on eBay. One is Kevin from vslcd http://stores.ebay.com/chinatobby?_trksid=p2047675.l2563
. He can actually sell you a whole kit but he won't be able to help with the PixelQi. As far as I know, PixelQi is the only company making those types of displays.
Maria from njytouch http://stores.ebay.com/njytouch?_trksid=p2047675.l2563
is another source.
Kevin is more technical and can help a little more than njytouch.
If you need any help or have questions just let me know. I've done hundreds of these and each project is always a little different. What I typically do is make a mounting plate and the LCD mounts on the top side of the plate and the electronics mount on the back. You can then mount this plate into an enclosure which makes a nice clean custom look.