Spool ends are a straightforward lathe-made part, if the design allows grip by a 3 jaw chuck. My design has a recess on the back side that lets the jaws grip in either the normal or reversed position. I use reverse position for the jaws so the grip is on a larger diameter. I make the recess by milling, before turning the front side profile. This recess requires a plunge cut, which is difficult to do with the lathe.
My design has a flat face, with a convex radius at the outer edge and a concave radius near the hub. The convex radius starts as a 45 degree chamfer which I then finish by lathe filing. I roughly form the inside radius by stopping the lathe bit (during facing passes) at pre-calculated radii. Then I finish this radius with a custom tool made from a 3/8 inch diameter carbide cutter (see previous post, on end plates). The cutter works quite well on Delrin, but less well on aluminum; I have to do a lot of manuvering to avoid cutting too wide a chip, since Sherline lathes have little reserve torque. I think that a satisfactory job could as well be done with the proper size round file.
I join the spool ends to the shaft with Loctite; see earlier post on spool assembly.