Try Forestry Suppliers Inc if you're based in a rural area. Receive
catalog by calling 1-800-360-7788. If you are in or near a big city
or university town, then I suggest your local yellow pages for a
graphics business that retails drafting supplies. I have purchased
both 8 1/2 X 11 sheets and large rolls of printed paper at a local
firm called Master Graphics. Some photography equipment distributors
also carry graph paper. Unfortunately, office products stores often
carry graph paper that is flimsy or inappropriately designed.