If you are handy, you can make some from Kydex.
(Mods, I hope it's OK to post a link to my site, if not, I understand)
http://www.triangletactical.net/2013/01/24/diy-shotgun-shell-caddies/
If you have a dremel, heat gun, and some other tools, its worth it, if not, you may be better off buying some. Doesn't Choate have some really inexpensive shell caddies out there now too?