This is a gem of a page that I just found, with lots of information about and examples of the titular quadruple ko and other no result situations.
To quote the introduction:
After the 2007-06-28 game between Kono Rin and Akiyama Jiro ended in quadruple ko, Nihon Ki-in wrote
This was the 19th occurrence of a “No Result” game in history. Nihon Ki-in has recorded 168,813 games from July 24, 1924 until June 30, 2007. No Result has occurred at a rate of once in about 9,000 games.
After the 2015-04-09 game between Kono Rin and Mitani Tetsuya ended in quadruple ko, Nihon Ki-in wrote
This was the 24th occurrence of a “No Result” game in an official tournament at the Nihon Ki-in. Eleven of them were from quadruple kos, ten from triple kos, one from a quintuple ko, and two from “eternal life”. No Result has occurred at a rate of once in 8261 games (0.0121%).
For the purpose of archival, I’d also like to share a screencap of the contents table. You never know how long these pages will last. Each game is linked to an SGF hosted on the site.
And also the final example.
A quintuple ko
Ohashi Hirofumi mentioned in a tweet a training match that ended in the quintuple go shown above. White has an unending supply of ko threats in the double ko at F1, F3. Black has an unending supply of ko threats in the double ko at G19, A17. Now they fight a ko fight at A2…