You cant get them anywherw, Those rollers on the magnus just basically break down over time and become really split and sticky and the plates when they are ejected get stuck to them,
Quick fix
I stripped both rollers right back to the shaft and put foam insulation over the cores like the stuff that insulates pipes and tied cable ties at the ends, was enough to drive the plate out, ended up getting both re-rubbered by Bottcher with same rubber as inking rollers, and have been working perfect for the last 3 odd years