I have been looking for one of these for ages. I had found some but could not quite bring myself to pay the money that people were asking for them.
I found this site the other day, http://www.uktactical.com/acatalog/W..._Drag_Bag.html and bought two. I was sure that they would be inferior quality bearing in mind the price. However they turned up this morning and they are excellent.
For anyone looking for this kind of thing I would say you will not get better for the price.