If you are going to make a ton of these, rotary broaching is the way to go. Slater or Somma will make the tool if you don't want to grind it yourself. I've got one a little bigger than that, probably fewer splines.
If this is for one or a few dozen, I've made a couple, two ways.
1.) Use a junk shaft, cut to lenght as useful, grind a slight pilot on the end and be sure the shoulder (where the splines are) is somewhat sharp, i.e., not ragged. Ram it through with an arbor press. The hole can be a little over sized as this is a partially extruding/forming operation like a fluteless tap. If the shifter is slit with a pinch bolt, do that operation last so it can tighten up.
2.) Use a dividing head & 4 jaw or fixture plate to hold the work, centered on the bore. set up on vertical milling machine and use the quill with appropriate tool to slot it out manually.
If your Haas has the capability, it should be a piece of cake.
smt