Just ring around, someone may have stock somewhere. Even if they don't have stock, I'd be asking to buy now to lock in the buy 3 get 4 deal, then ask them to just fit them later once they're available (assuming you can wait).
Also, just call around to any other shop you can think of. When I put AD08's on my Golf R, I literally called a dozen different places. Prices varied from $460/tyre down to $360/tyre (235/35/19).
My honest opinion, don't let the price scare you. For daily, spirited twisty roads, or full track days, nothing beats the AD08's. My last set even lasted 35,000kms - without any rotations either!
I have no idea where you are located, but if you're in Melbourne, try Associated Tyre Services in Cheltenham. They deal with Yokohama a lot, so get much better pricing that other shops.