There are second hand accounts from indigenous people, excavated bone sites with tools and spear tips, but reportedly no first hand recorded observations from Europeans of buffalo running off cliffs.
Buffaloes aren't exactly Main Battle Tanks you know: it's not that difficult to build fences that are able to stop them (it just won't be the light fences you have in mind).
Also, not voluntarily pushing the beasts to your fences is going to help a bit, since buffaloes don't run to cliff on their own…
Private cattle ranches could never have competed with 30 million bison owned by nature, free for anyone to take.