http://www.mangago.zone/read-manga/dousei_yankee_akamatsu_seven/
this one is really good its not mafia or yakuza per say but there is a gang like atmosphere
It's not yaoi but http://www.mangago.zone/read-manga/gokusen/
Ahhh thankyou all
http://www.mangago.zone/read-manga/dangerous_convenience_store/
http://www.mangago.zone/read-manga/the_boy_and_the_wolf/
http://www.mangago.zone/read-manga/madman_combo/
http://www.mangago.zone/read-manga/naked_sword_and_tree_peony_of_black/
http://www.mangago.zone/read-manga/funky_yankee_baby_kun/
http://www.mangago.zone/read-manga/because_love_exists/
http://www.mangago.zone/read-manga/moon_and_sun_abe_akane/
http://www.mangago.zone/read-manga/2b_b_boy_badboy/
http://www.mangago.zone/read-manga/simplified_pervert_romance/?39ZW
http://www.mangago.zone/read-manga/haga_kun_wa_kamaretai/
http://www.mangago.zone/read-manga/megumi_and_tsugumi/
Yaoi manga with goofy yakuza / delinquent characters.