Triad Tactical is a GTG and recommended vendor, but they show out of stock as well. You might call the factory. The EI website lists one available in black, and one in khaki.
Sigma bags are my primary travel bags, and have been excellent. Highly recommended.
I also suggest you check out the LBT medium and large loadout bags. They are more expensive, but like Eagle, LBT is worth paying for. Do note that they are a couple of pounds heavier than the Sigmas. If you fly, the large also exceeds the allowable linear inches for baggage on some airlines, but not a noticeable amount and may get by. Big plus: Both the medium and large are available in non-mil colors, burgundy and forest green. Check them out here:
LBT also sells excess and/or very slightly out of spec gear on eBay. I have bought a pair of hydration carriers for $25, and a loadout bag in burgandy for $40.
I actually emailed Linda in Virginia Beach, trying to find the issue on the hydration packs. She said there was a slight misalignment on one of the MOLLE rows. I would not have found it withour her mentioning it.