L & L Insulation & Supply 1705 Sulphur Ave St.Louis, MO 63110
314-781-9991 Ask for Cindy Goetz.
One note though, They were supposed to e-mail me with the exact price but never did. My wife got a call from FedEx stating they had a delivery and needed cash or money order.
You're in a fairly large city, you should have no problem finding foberboard, even if it's not the OC brand. Just try the yellow pages, try commercial insulation/HVAC supply etc you shouldn't have trouble finding it with a few calls.