Military Messenger Bag Where Can I Find This Messenger Bag Everyone Seems To Have?

Where can I find this messenger bag everyone seems to have? - military messenger bag

I need a messenger bag, and put my documents, etc., with the strap of a secure "by the body"! I am very simple, but I can not find it! It is very small or juvenile. A simple military khaki or green would be perfect! but the road is a sad choice!
Suggestions?

Thank you.