Pixiv booth, Comic Zin, Melonbooks, any used doujin store (like surugaya). I actually bought two copies of each one because I tear apart one copy for scanning...and I've since learned that her digital copies range from good quality to awful which is why I kept away from them mostly.
On an on topic note, there's quite a few tamamusi doujins you probably won't ever see scanned as used copies go for up to 5000 yen...unfortunately I didn't have enough foresight at the time to buy two of each. It's incredibly rare to see the price on an artists work get that inflated. I witnessed the day it went from 500 yen to 5000 yen lol
Good luck with buying doujinshi. If you can gather even a fraction of what I have in my collection, you could gain a smidgen of insight as to why I don't want to continue doing this for now...not like I've stopped collecting though, just got in an order of 20 doujins which is super light for me.
(PS out of good faith part 2 is DMT related...shrug)
