Found this suprisingly kind of promising looking headband mod on aliexpress For KOSS Porta Pro, KSC35, KSC75, KSC55 : r/headphones
Amazon.com: Voarmaks Light Version Headband Head Pad Top Foam Cushion Ear Pads Compatible with Koss Porta Pro PP KSC35 KSC75 KSC55 Headphones Portable Featherweight HeadBeam : Electronics
Refit DIY MMCX Cover Balanced Cable For Koss Porta Pro Portapro Ear Pad Headband Foam Cushion 64 Ohm
Koss Porta Pro "Beached Whale" Mod (desc. in comments) : r/headphones
How to do the Headband mod for Koss KSC35 Headphones and Koss KSC75 Bluetooth headphones - YouTube
Headband Head Pad Top Cushion For KOSS Porta Pro PP KSC35 KSC75 KSC55 Headphone Portable Featherweight Version - AliExpress
3 portable on-ears: Koss PortaPro, Senn PX100-II, AKG K403 | Super Best Audio Friends
Head Kore 87 Review|koss Pp Headband Replacement - Metal Cushion For Portapro Headphones
KSC75 on a Porta Pro headband. Something about this simplicity, porta(heh)bility and comfort makes me want to use this combo more than my HE400SE, KZ ZSN Pros, or my Akg M220. :
Silver & Gold modded MMCX KSC75s with PortaPro headband and Yaxi Pads : r/headphones
Taking Koss Portapro to the Limit (cool mods). | Page 3 | Headphone Reviews and Discussion - Head-Fi.org
Koss Porta Pro | Wireless Mod | Retro headphone, Koss, Koss headphones
Koss Mods | Headphone Reviews and Discussion - Head-Fi.org
Headband Head Pad Top Cushion For KOSS Porta Pro PP KSC35 KSC75 KSC55 Headphones | eBay