Pictures would be good to identify if its spline or involute spline.
If its non involute a tool can be made to recreate spline.
Maybe easier to see a gear cutting specialist
I saw some half shaft splines that had been home made. The splines were cut with a cutter that had a singleWhen I lived in the Philippines our local machine shop would duplicate any sort of spline with a dividing head and a hand ground fly cutter, on a horizontal milling machine. They were surprising good quality.
The only let down is they could/would not set any sort of stop on the length, so every flute was a different length, which looked messy.
They made me a drive shaft for my V8 bike, but I never tested it anger much.