Here you can see that the sandtroopers in A New Hope was ammo packs on their shoulders.(and some wore them on their belts as well)

They are have identified as MP-38/40 mag pouches from WWII.  You can buy them here, but you'll have to die the leather black.(from green)

The ones on the left are the "MP-38/40 Mag Pouch Set (Norway, Post-War)."

The store above seems to be sold out now, but there's leather versions on Ebay occasionally.  I picked this single pack up for around $15.

The back is greenish, but the front almost looks as if it's already been altered.  I might not have to even do anything to it!  What a find.

Again, expect updates once I get around to mounting it.

<coming soon>

To attach it to the armor, I basically ran a black strap through the pack's straps & around the chest plate's bridge to the back plate.

I found a fairly nice case for the Nintendo DS handheld system.  You can kind of see the logo on the front, but after some colored sharpies & weathering you'd really have to look close.

For the Imperial logo, I simply printed out a stencil & used a silver sharpie.  I needed to use some space IS Velcro to extend the pouch's belt loop.