i've seen auctions on ebay for 703 from a couple of sellers recently. i'm not sure it's the greatest deal though. i've seen a few different auctions, for like 6 sheets of 24x48x2 for about $100 shipped.
I just thought I'd mention to anyone else who's seeking OC 703 and can't get it for whatever reason. I used an alternative to the 703 and Rockwool. Armstrong ceiling tiles (#420), they are rigid fiberglass but are about 5/8 inch. On another forum Ethan Winer gave it the green light as long as it was stacked to be 2" - 4", pref. 4' for bass absorbtion. 16 come in a box, just tear off the decorative paper, glue a few together and wrap in fabric. For $55 I got (4) 24 X 48 X 2.5 pannels. I also got ichy as hell but they work pretty well.