Everything DX7 and DX6 is now on backorder!
The easiest way I know of is to go to http://www.horizonhobby.com/
and search for whatever you are interested in. Just now, everything DX7, AR6100, and DX6, and AR6000 show BACKORDER. Some show availability dates, but not all do. All you can buy just now is the bind plug, one of which comes with each receiver!
I heard earlier that they were having some trouble with their supplier of AR6000s. Now it looks like everything is BO. That's not a good sign, IMHO! At the very best, it's a symptom of too much success.