Canbnot help you with that except to say that ASC (Agri-Supply) sells the friction plates as well as the required steel plate for various makes of slip clutches. Keep in mind that any slip clutch will be high maintenance as they have to be 'slipped' every year as the plates will bond to each other as well as the metal disc if you leave it sitting outside all the time and that entails backing off the load springs, slipping the clutch plates and then resetting the load springs to the required torque break which is a PITA, always.
I have no idea what tractor you plan on mounting it on but whatever you mount it on, I would suggest purchasing an over running coupler to but on the end of your PTO stub (ASC sells them as well). The reason being is that any shredder will have a lot of kinetic energy in it from the spinning blades and if you disengage your PTO at speed, the shredder will continue to drive the disengaged PTO and your clutch brake that is internal to your tractor will attempt to curtail the rotation of the PTO stub and will fail prematurely. I always run an over running coupler on my PTO stub when running either of my shredders, with the bat wing or the solid top. Most all my hay tools have built in over running couplers in the drive lines, but not the shredders so I add one when using them.
Just an FYI for you. If you destroy your internal PTO brake, the stub shaft will rotate constantly due to parasitic drive from the gearbox in your tractor.
Again, I have no idea what make your tractor is and it really don't matter. Adding an over running coupler to the PTO stub is just good insurance against PTO clutch brake failure from inertia driven loads.