REI or SorrEI (sorry E I) as I call it does have some good stuff just nothing specialized for bikepacking and they do tend to be more of a clothing store with some out door gear to get you in the door.
Campmore has a web site as well as a catalog they have a mix of quality and cheep stuff but again no real bikepacking gear.
I got my seat bag right from Eric at Epic there is a link in the review section on this site I don't think either of the guys making these things have any other outlets yet.
Then there is Golite
http://www.golite.com/main/home.aspx and I am sure there are other ultra light back packing sites most of that stuff works for bikepacking as well. As of now I don't see any one trying to cater to our small market.