The Graphic View series used the same lens board that many other press and view cameras of that time also used. They should still be plentiful. They are also easy to build up with two square pieces of properly sized 1/8 inch plywood or other material. The front piece is 4" square. The back piece is 3.5" square. Since the back piece is merely a light trap, it can be made of foam core, foam rubber, thick felt, or almost any other blackened material. If you have the tools to cut the hole for mounting the lens, fabricating the board should be no great problem.
It's called a "C" board. The same one used on pre- Pacemaker 4x5 Speed Graphics. They should be pretty common, or as other have posted, they're easy to make.
Back when all High Schools taught woodshop, a box of fresh doughnuts to the woodshop teacher and he would probably make you what you need out of scrap.
I have Graphic View, Graphic View II, and Anniversary Speed Graphic cameras -- lens boards interchange between all three. One of the reasons I like that set...