My research a few months ago turned up the same as yours. Apparently they are custom items. You design it & get a tool & cutter guy to make it up for you. I have been looking in to engine porting; found an Iscar cutter that is really close to a lollipop cutter. I have also discovered having a 5-axis machine, a cutter and some CAD software leaves an awful lot of other steps to cover. You need to digitize the part, move it to CAD. massage the data, have a suitable post processor, etc., etc., etc., before you can port heads. My project is on hold until I can close the gaps.