I bought a few boards for my Century Graphic a few years ago. I'm pretty sure I bought them from Midwest Camera Exchange. IIRC, they were pretty reasonably priced. Probably worth an internet search.

If you can afford it, buy a few lens boards. I have acquired several lenses over the years that really shine on the Century. Besides the premium lenses (80/2.8 Xenotar, 105/3.5 Color Heliar) I use a Kodak Special Anastigmat (four element "uncoated ektar" from a Kodak Monitor) and a Zeiss Kodak Anastigmat (unmarked focal length -about 160mm/6.3) and a Tominon 135/4.5. Each lens gives a different effect, and are great fun to play with. I have one lens board left. I'm trying to decide whether or not to mount an 85/4.5 Apotar (an amazingly sharp triplet) on it.