you have a 50% chance on drawing him with an average of 1k seal scrolls in GNW treasure. that means 1-2 years of saving, or 125000-250000 coupons if you're straight up buying seal scrolls (not recommended).

Naruto [sosp mode] on the other hand is (technically) easier to get since he has been events for 20k, but he hasn't shown up in coupon events for a very long time now (and might continue to not show up at the rate things go). you could uh...collect him 1 frag at a time when he pops into time-limited treasure or colourful balloons events.