Basically do all available daily events and activities, sealed ninjas twice a day, check hot topics if there are scrolls as redeemables. As for events itself, almost every week there are events, that award seal scrolls (sometimes 1, sometimes more for jsut participation), also lucky board, stars event tend to give quite nice ammount of seal scrolls as an addition when u use coupons. GNW packs are also one of the best sources of seal scrolls. After that, once you decide you want to pull from X treasure, ALWAYS wait for seal scroll rebate that awards permament scrolls. After using 300 seal scrolls you get 66 for free, thats crazy high ammount. It's an equivalent of 120$ recharge if you actually wanted to buy seals from the shop.