Where can I find paper/aluminum foil sheeting that goes behind the drywall of my bathroom?

In tearing down the drywall because it had gotten soaked due to a water pipe leak behind the drywall, I found that a sheet of paper/aluminum foil was installed behind the drywall. I'm uming that this sheet was originally installed as some kind of a barrier to the outside concrete block wall that it covers. Now that I have to replace the wet drywall, I tried to find out where to purchase this sheeting to no avail. Home Depot or Loews do not carry it. Is there anything else I can use, instead?