Yes, most CM's or CueTechs should be able to bore and tap a 3/8-10 modified hole in your shaft for you. I'd recommend going ahead and having a matching black collar put on the shaft as well to protect it - your call. Then it will need to be turned down to match the butt and some finish placed on the first 4-6 inches.
The CM is also going to prefer to have your butt, 1) so he/she can match the joint diameters exactly and 2) to verify that the pin has been installed dead-center in the butt.
I'm guessing you already have the partial because otherwise you should be able to buy a 3/8-10 shaft of your choice with no problem. It might still need to be turned down, and a little finish applied, but that's a lot less work.
We're not allowed to post pricing on this forum, so you'll need to discuss that with your CM/CT.
HTH,
Gary