In the first game I recall rerolling quick respawn glasses with three ink saver (main) abilities as my first triple from rerolls - and it was my favorite glasses so I was extremely happy about it. And I had a gearset made with triple rerolls full of special charge up main/sub and special duration up main/sub abilities only - and I can tell using an echo weapon with that was a blast :D
I don't reroll in Splatoon 2 anymore. But as for getting lucky while leveling gear, every time I try to farm ability chunks I get a triple per grinding run (or sometimes more). As of now I have
three shoes with triple ink recovery subs - the main abilities being ink recovery up, ink resistance up and special charge up respectively. And I also have two more shoes with double ink recovery up
Other noteworthy random triple is a special power up on a special power up main shoe (an
amiibo shoe!). But sadly the combinations of my lucky triple gears aren't fresh at all in looks..
Considering my very low hours so far spent on chunk-scrubbing, it is quite something though!