You can have the TRE reamed to the correct size and taper and I have heard of having the splines drilled out and the splines from another arm welded in, but having a whole manufactured from scratch, I have not seen. If it was flat I suppose it wouldn't too difficult.
Making a new Pitman arm would be about the most difficult solution to this dilemma I could think of, and would still not solve the problem. Your problem is NOT the Pitman arm, but the drag link, or relay rod as you call it. If your hi-steer uses 1-ton tie rod ends (TRE), they will either have 7/8 or 1" threads -- way larger than could ever be mated to your OEM drag link. You need to have someone make you a new drag link that is large enough for 1-ton TREs (I use 1.375" o.d. DOM with a .375" wall). You can then either ream out the Pitman arm to fit a 1-ton TRE, or use a smaller TRE on that end -- like one that already fits the Pitman arm. Often on these custom steering setups you have to spend some time coming up with the right TRE for the particular configuration.
I have already tried reaming out the pitman arm. But of course, there was maybe a 1/16" of an inch around the outside of the hole, so I did not even try to put it back on and drive it.
I guess a new PS setup would allow for a pit arm that will accept 1ton TRE and get rid of relay rod. I currently have the toyota setup, but I still have the factory relay rod running down the inside of driver's side fender, stock pitman arm, etc.
Should I go saginaw and do away with toyota?