In Konoha Outlets you can buy pack. 42 coupons, gives 1 page and 1 mantra elixir.

That's the only way I know for now

Konoha Outlets, Total Recharge Rebate, or Fuku Deals. Other than that, wait til next week.

Hello!

Just like what other users said above, as of now the only way to obtain Secret Scroll Page and Mantra Elixir are from the events of Konoha Outlets (at 42 coupons per pack), Total Recharge Rebate (if you recharged) and from Fukurokumaru's Deal. Thank you.

did someone check the stat boost already? is it worth spending for?

Also wandering how much power per cps is it

In my own opinion, secret scroll is worth spending for since it will increase you initiative if you reach the highest level which is 19.. But I wont spend though.. hehe

Do the stats carry to Arena?

Well since you need to know that only initiative counts in arena then yes, secret scroll does help out in arena

Hello!

Like what Danzo said above, yes. I do think that the Initiative Stat carries through Arena. And about the coupons = power question, I haven't tried spending on this event to the fullest but I did try it on my other account. 5k coupons worth of Secret Scroll Pack from Konoha Outlets made my Ini+LR at Level 5 and Ini+TP at Level 3, total power I got is around 2.7k. Spending coupons for the new feature? No, I won't for now. In my opinion, the cost is high and the gain is not much, Training Potion is still the best (up to Level 8s to 9s, 10s if you can spend more).