That's why I've learned to multi-task. If I find a good deal that I'm able to move on, I place the order with one hand, start firing off texts with the other.
So far as what you're looking for, all I can think to do is just stalk websites and pray. Just checked ArmsList, and the cheapest M&P 15-22 listed is used and has tan/desert furniture, and the guy is asking $600 for it.