Do you want a bag to carry a bunch of stuff, or just one to hold magazines. I have one from here, worth the wait:
http://olongapooutfitters.com/index....d&productId=37
and more on order.
Like it says on the site, it's like the bag the Minuteman would use to hold powder and shot next to the musket.
For a carry-a-bunch-of-stuff bag I just use an old range bag. I got it from the local Army-Navy surplus store.