I don't know if you'll really find a "source'. SignComp and others sell kits for directional
signs, but these are an easy manufacture. They look like your run-of-the-mill directional
sign fabricated from 2" square aluminum tube frame/supports and overlaid with .063" or .080" aluminum. Your dimensions indicate they're 5" deep. They don't look that deep (again, I would assume 2"), but if they are 5", it's still an easy job if you have basic tools. If you don't have the means to manufacture them, contact Kevin Crutchfield at Casco
Signs. He's pretty close to you (in Concord).