Lathe Tooling for Retaining Rings

[wilsonmw04]

Greetings,

We are working on a fall project and want to try out retaining ring of our axles.
We are using a 3/8" and 1/2" retaining rings. According to Mcmaster we need to cut a 0.029" and 0.039" wide grove in the shaft for them, but our lathe does not have a small enough bit. Do we need to grind a larger cutting tool down to size or can we buy a COTS items at that size, if so, where?

Thank you for your help in advance.