Victor was right, PFab coolant reservoirs are once again available. I don't know if any of our sponsors here are selling them but I did see this thread on modfords.
http://www.modularfords.com/forums/f17/pfab-intercooler-reservoir-tanks-stock-lethal-87644.html
http://www.modularfords.com/forums/f17/pfab-intercooler-reservoir-tanks-stock-lethal-87644.html