Where do you live? There a several places online you can buy it. And also digital versions are available too.
In my country, there's no enough mangas for sale in comic bookstores especially BL ones. They mostly sell famous mangas like One Piece, Naruto, etc. Thank you for the link. It's super helpful! <3
You can get them on bookdepository.com and they do free shipping worldwide
Sorry for late reply. I will do this one. This is more effective than waiting and looking around bookstores. Thank you very much.
I LOVE this manga so much to the point of looking for the original manga in English translation to buy, but no luck. I want to buy the whole series and proudly show it to my otaku friends who can understand my fujoshi tendencies. XD