I've found a few but was wondering if anybody has better luck at finding different ones.
So far I've found..
GPAŽ Backpack | Dover Saddlery
^ Same backpack, the second link is a lot cheaper but I'm not sure about the website..
Equestrian M Series Backpack (Black) - GearMax - Online Store
Grand Prix Rider's Backpack | Dover Saddlery
Does anybody know of any others or have experience with these?