He first showed up in a recharge/spending rebate I believe (40k)

Then he showed up in lucky stars that one week where every other Joe pulled him effortlessly

He was also in lucky * I believe part of the Hokage option packs

and yes last year in treasure of the sage, base price was 300 cps I believe, 10% off was 270 cps, 20% off was 240 cps, etc

but he's yet to appear in events since his kit changed. possible oas wants to "balance" the game and doesn't want everyone running around with a minato? who knows