My Oppo Pm-3 pads were falling apart, but I couldn't find a replacement. ATH-MSR7 pads fit nicely, but you'll need to tear the original pads apart & keep the plastic base. Carefully
Oppo Ear-Pads Listening and Measurements | Stereophile.com
PM-3 Replacement Earpads | OPPO Digital Australia
Oppo PM-3 : The Portable Planar - Impressions | Page 391 | Headphone Reviews and Discussion - Head-Fi.org