Okay, don't shoot me, zahn, but this is for a lawnmower ...
Take 3/4" piece of steel bar, braze a piece of high speed across the bottom with one edge across the centerline, hand grind the shape to match your male sample part then stick the thingy in a collet on the Bport and cut your shafts with a dividing head.
Find an old-fashioned boring bar with the square slot in it, straight across not the ones at an angle, grind a segment of high speed to match the internal, then rotary table and hand slotter it in the Bridgeport with the quill handle. Light cuts. Very light cuts. Luckily 9 goes into 360 evenly, it's a bitch if you have to keep track of minutes and seconds
As long as you are only making a couple, this'll do it and won't cost anything. If you use 7075 aluminum for the female and have it hard anodized, it should hold up pretty good while still being easy to machine. Or steel, I guess. 8620 will cost a minimum charge to carburize ($50 ?) but it'll last a lot longer. Still easy to machine. Prehard 4140 and all that, eh. Not my preference but whatever you like, might save a few bucks on heat treat and if your time is not hugely valuable, why not ? Won't hold up as well as carburized though. I guess you could kasenite it yourself, might be kind of fun.
Plastic is real easy to machine but you already know how well that holds up
those are flat root, btw.