Where do I get SQ?

Uhmm... Credit Card

Daily and total login bonuses too, plus apologems and commemorative gifts. Once clearing the free quests it takes a while to get many free sq.

Login streaks and master missions are the most reliable. Downtime apolgems usually give 3 unless it's a longer outage. Events sometimes have 1st clear rewards on some quests, but not always as they usually offer apples. Celebrations sometimes come with SQ for hitting certain twitter/facebook targets. Free, interlude (unless they reward a skill/NP upgrade, I think), and rank up quests usually offer them as 1st clear rewards.