I got tired of paying the high freight costs years ago, custom made a machine for routing and shaping wood stringers and it works great. I start with 3/4 X 3/4 Sq. fir good quality clear door stop material. I run fifty or sixty pcs. at a time, let them sit for a few weeks, a small percentage will twist and warp. If they are still straight after a few weeks they will be straight for ever.
I prefer wood over aluminum. If you are struggling to move your cub in deep snow, and accidentally push on the side and bend an aluminum stringer it is almost impossible to straighten it. If it is wood it might crack or break but you can get inside and splice it, and from the outside will never know it was damaged. The profile of the ones I make are like a mushroom and are slightly stronger. Also when I am installing the fus. fabric with the seam down the back, I can use map tacks to hold the seam to the stringer while the glue dries. It helps keep every thing straight. I have used wood stringers for over 25 years and the aircraft that I used them on are still as straight as the day I installed them.
I would take a sample of the original to a local company that specialize in wood working and get a price on having them make/ copy them. Have them make some extras in case of fitting mistakes or warpage.