The ways to earn coupons which I can think of are these:

Weekly/daily sources

1. convoy and plunder 910 cps.

2. daily log in 70 cps.

3. group summon 160 cps

4. group wheel average 20 a day so 140 a week.

Monthly sources:

5. daily log in 250 cps.

Seasonal sources:

6. myoboku trial 420 cps.

7. wishing lantern 140 cps.

8. weekend events average 80 cps a month.

9. zenith 200-3000 cps.

Random sources:

10. survival trial 20 cps a month (?)