I'm puzzled. The ribs/frames on my Tradewind are C-channel 1 1/2" x 3/4" x 1/16" extruded. I think you could buy that locally, not from Home Depot, but from a metal fabricator. Freight would be a killer if you ordered from Aircraft Spruce.
The girts/longitudinals on my Tradewind are C-channel 1 1/2" x 5/8" x .032", bent on a press brake. You could get these made by a local sheet metal shop, but you may need to supply the sheet metal if you want it made from 2024-T3.
A metal fabricator could also roll the curves in the ribs. Best to cut a pattern out of cardboard and they can duplicate it.
The fabricators I deal with appreciate a bag of donuts about 9AM.