Try these guys - Supply Captain. Look in the Store, then ITW Nexus - all sorts of clips and buckles etc etc and pretty cheap too. Email them that you're military and you get a 10% discount. Quick delivery from USA too.
The manbag is the dogs balls if you're a commander. All your maps etc in one handy to reach place. If you're just a grunt, then personally, I don't see the merit. I used mine once then slung it in my box. The assault vest I had did the job fine.
Be very wary about wasting your money on it. As I say, unless you're a commander, it's not doing anything a good vest can't, and it's also all your eggs in one basket. So god forbid you have to bug out asap and you leave it behind. At least with an always on vest, it's not likely you'll leave your torso behind. (Unless it really has gone wrong)
I think the idea behind it being a grab bag is that you grab it an scarper.
It hold 9 mags which with the 6 or so you carry on your osprey, thats your OP ammo sorted. Not many people wear vests over Osprey, just a few pouches for bullets on the front. A daysac with the grab bag under the lid = pouches to keep the ammo in one place. If your down 6/7 mags, your in the popo anyway. And maps, water, GPS, Leatherman NVG can all be stashed in there no dramas.
So is there any more gen on getting these issued, I am seriously thinking about one. I have got a good modular chest rig which is great over Osprey. But I am a team commander for Iraq, and the shit we're gonna need to carry keeps mounting, the idea of med pouch, ammo pouches and a camelbak on osprey plus this man bag is starting to sound more and more attractive, I am after, informed opinions if there are any. ANyone used them in that sort of set up, what are the thoughts. And can it be sourced through the system or is it just talk?