Fulfillment Supplies - Lots of sizes from 24X24 to 48X72 - All for less than 1 cent a square foot.
I tried many keyword combinations
36X72 cardboard sheet
48x96 cardboard sheet
48x96" cardboard sheet
Anyone with additional sources please let me know. I will be buying these within a few days.
I found an additional site - Pack and Seal they carry the 4x8 sheets for about .8 cents a square foot. I still ordered the 4x6 sheets from Fulfillment Suplies at about .73 cents a square foot..