He's actually not in any cps redeemable events. He is, however can be collected over time without spending cps at all. What you have to do, is save up your seal scrolls and wait for recruitment feedback events. Save until you have 734 ss in your inventory, and when recruitment feedback is around, pour it all into gnw treasure. Why 734? Because you get a total of 66 ss from using 300 ss during recruitment feedback event, so you'll actually be able to reach 800 ss use and get the 5 Edo Hashi frags from 500 and 800 ss use as well. As for Edo Hashi drop rate, every 40 ss used (free draws included), you'll guarantee to pull either 1 or 2 of his fragments (800 ss use gets you over 30 of his fragments, exact number varies). Keep that in mind when doing the calculation to determine how close/far you are from him (1600-3200ss range in total). But he's usually requires around 2k ss as stated above by someone else.

As for how to collect ss, well, you get 2 each week from monthly events (300 monthly points each week needed), so 8-10 a month from monthly event, you get 2 ss each month from check in everyday (the 5th and 17th check in). You also get ss from matsuri on Monday and Friday (need 4 wins, though), so another 2 each week if you're lucky. You may also get ss from swb if you're in the top 3 on your side, so probably not likely for most people. You may also get ss from gnw packs, if your group is active and you attend gnw, group leader may gives you packs which gives 5-8-10 ss. If you manage to reach 6path in arena every month, there's another 6 (or is it 7?) ss in mail the beginning of the following month (actuall ss fragments equivalent of said amount). Being able to be in space-time matches (top128 space time ranking) also gives ss. However, you'll need to win at least 1 match. After that, how many ss you can get depends on how far you can go. Other than that, it's about ss fragments collection. Sometimes they're sold in blackmarket fir coins, you can trade for them in space-time exchange shop, you can spend spare sun coins on them (I usually go 6 charm boxes, 18 adv refs, and 2 ss fragments each week). Collecting ss is time-consuming and requires good planning and active playing in general. But you'll get there eventually. Also, don't spend cps on ss unless they are discounted by a lot, you have a lot of cps to spend, and you're super close to your saving goal.

5 Edo Hashi frags is the equivalent of 120-200 ss used, though, so by saving for 500 or 800, you actually reduce the total ss needed.

Actually, if you get 2 frags every single time, you'd get 80 frags at 1600 ss used since it's once every 40ss, so 2100 is entirely possible. Unlikely, but possible.