I finally found the hatch gasket material if anyone ever needs it.
Found it at a company called McMaster-Carr - www.mcmaster.com
The foam comes in 2 types, EPDM and neoprene. Don't really know the difference, but I got the EPDM. Had to buy a 100 foot roll, but that will replace all the hatch gaskets on the boat (twice). The roll was $25.00.
My boat (Irwin 37CC) used 3/8 inch round cord.