I bought a few of these from Evemodel.uk on #bay. They are ' Half radius with bearing ' Just pick the correct radius and they arrive from China fairly quickly. You will have to run the bearing on a template. I have to say the quality seems fine and I had no complaints.
I make my own for my spindle including handrail profiles etc. Fraction of the price of bought spindle or router cutters and exactly match any profile.
It's fairly simple - you need a 6" bench grinder and 4 wheels: 1/2 and 1/4" and same again with half round profile.
Angle grinder handy for roughing out.