If you have access to a table saw, you can make them out of 1/8" hardboard. A 4'X4' sheet available at the lumber store sure makes a lot of lens boards. The hole can be drilled with a hole saw in a drill.

Get yourself a speed graphic with the older style flat lensboards (not the stamped steel boards), and you can interchange lenses from your speed graphic and Enlarger. Some of the old enlarging lenses make very interesting images when used as a taking lens. I have an enlarging ektanon that, when used as a taking lens, is very sharp in the middle, tapering rapidly to blurriness and swirlies at the edges..