I purchased a pair of headphone pads on Amazon that were advertised to fit my Sennheiser 598s but required some modification. Recorded the mod if anyone needs to do a similar change.
These are the pads in question - great fit and comfort after the mod:
www.amazon.com/gp/product/B00ZGGG3KY/ref=ppx_yo_dt_b_asin_title_o00_s00