Best event to get him would be lucky board or missions mobilization since you can get power items from them too, however he has not been in either event for months. Currently you can get him for 9600 cps from treasure of the sage at 40% discount, or from fateful choice where his price is around 12k but you can get another cheap ninja and some power items from fukurokumaru deals which normally comes in the same week. Up to you what you want to do or if you think the items from fuku deals are worth the extra 2-3k cps (is very worth it in my opinion especially if you can get another decent ninja for spending 5k like we had before). You will need to save all your coupons for 2 or 3 months to have enough for him.

You forgot myoboku trial and wishing lantern which is 560 a month and daily log in which is 250 per month and weekend missions and occationally coupons from survival trial which is another 100 or so. Plus many f2p can do plunder maybe not daily but if you can do it successfully 10 times a month that is another 500 coupons.