Going to try a 3D printed one using ColorFabb HT, we've got a little bit left from another project, but I may need to order some new.
http://colorfabb.com/co-polyesters
Added a load of extra structure to strengthen the part were it’s bolted.
The print is sliced like this giving the most strength in the direction the force of pushing the clutch would go through the part.:
The yellow lines are the movement of the print head, the black cylinder is the print head, it's shown with the top 1/4 left to go, the corrigated stuff is support material - without it gravity can take effect and the runs of plastic can sag. It's set to print with 100% fill so that it's as strong as it can be. The prototype had less fill which saves both print time and plastic but is not as strong.
If it doesn't work I can still make a metal one!