Is there any materialX node to get a radial or circular ramp? If not how could I go about making one?

One way is to use the attributepaint node. Click once in the center to generate a faded radial mask attribute. Then you can use that mask to drive a ramp in the color node. Feed that Cd or mask into the MTLX shader to drive what ever parameter you want.

use the length node for radial and atan2 for sweeping circle