So each volume of BSD has its own two-pages omake (extra), vol 19 is the latest one, which means that there've been 19 omakes so far. Thus I made this list for those who want to read them ^^
Omake 1, 2, 3, 5, 6, 8, 11, 12, 14, 15: https://yeouya.tumblr.com/tagged/bsd-oma...
Omake 4: https://akutagawaprize.tumblr.com/post/1...
Omake 7: https://fukasenanairo.tumblr.com/post/14...
Omake 9: https://dazaiscans.tumblr.com/post/14444...
Omake 13: https://akutagawaprize.tumblr.com/post/1...
Omake 16: https://judaluffy.tumblr.com/post/182085...
Omake 17: https://chazukekani.tumblr.com/post/1876...
Omake 19: https://popopretty.tumblr.com/post/62254...
So the missing ones are omake 10 and omake 18. Omake 10 are the pics of this post, translated and edited by me since I cannot find the English translated one, and guess what? I don't speak Japanese, but luckily BSD is currently published in my country, Việt Nam. I bought every volume and they all had their omake attached. So, yeah, omake 10 here is brought to you i...