Just flanges is probably a perfect first project - what motor are you looking at?
If you’re already working with them it should be easy to duplicate. We were originally going to work off of a gasket, but doing it from a part is the same. If you want to PM me some basic specs (desired material/thickness and a square dimension, i.e. 2" high by 14" wide) I can run numbers for sourcing some material and see how you like the projected cost compared to what you have already, do a run to see how you feel about the quality and go from there.