You need a machine shop, not a shop like Bimmersport, RMP, etc. As they probably outsource all the machine work and ate probably only interested in the labor to install it.
PM Natorious VR, he seems to know his way around turbo m20s. He may know the right people who have done what you are asking before, which is what you want. You don't want some machine shop learning how to o-ring your block or weld aluminum on your head.