Can't you model one? A search on Google shows several different spline styles. If you know the spline style you need...
Good idea!! I did not think about doing it that way. I'll try it out.Use the picture you have, import it into an Alibre Drawing then trace a sketch around it. Copy that sketch and paste it into a model sketch to extrude and create your model. If you know the diameter of the adjustment screw head that will help you get the size correct by scaling the image before you trace it.