It'd probably be helpful to have a part number or/or manufacturer. Do you have the paperwork? The STC for that mod should have the p/n. If not, Arkansas Dave has a similar set-up on his 170 to drive the supercharger. Maybe he has some paperwork with a part number.
The P/N is D6-2-2 (Split Sheave). I think the best bet is to call AVIALL; it is an Airborne Kit No. 312 I have rev K dated 2/20/86. It will be spendy . Or call all the salvage yards...