Volume 25 Bonus Chapter (and Extra Illustrations) : r/OnePunchMan

One-Punch Man, Chapter 34 - One-Punch Man Manga Online

Some extras from volume 26 (Low quality) : r/OnePunchMan

Volume 23 Illustrations [HQ] : r/OnePunchMan

Volume 25 Bonus Chapter (and Extra Illustrations) : r/OnePunchMan

Leaked Volume 27 bonus chapter [Shitpost] : r/OnePunchMan

Vol 27 will have 192 pages, it probably only contains these 6 chapters that add up to 186 pages, those remaining 8 pages could be cover, illustrations and hopefully an extra chapter of 2-3 pages. : r/OnePunchMan

One-Punch Man, Vol. 25: Volume 25 by ONE

One-Punch Man, Vol. 23 : ONE, Murata, Yusuke: : Books

An old character seems to be doing well (vol 21 bonus chapter spoilers), /r /OnePunchMan, One-Punch Man

One-Punch Man - MangaDex

Volume 25 illustrations [HQ] : r/OnePunchMan

All illustrations and bonus content from volume 26 : r/OnePunchMan

Chapter 31, One-Punch Man Wiki