Back with this pictures
Tha wide shape of the pouch looks to me like a cartridge box or a double pouch. Cartridge boxes have the closing rivet normally at the bottom. Not on the front, some double pouches have these but this pouch looks not like its splitted in two pouches. At the side to the backpack there is a rivet in the lid, at the side to the front there is no rivet. The side shape looks a bit like a triangle.
I hope that helps to find the original pouch, sadly I think it's a overworked pouch...
Best regards