http://www.mangago.me/read-manga/kyokutou_no_hanamuko/ ch 3
totally captivated
cAt has a list that all yaukza.
http://www.mangago.me/home/mangalist/5383/
Mine list is mixed : Yakuza ● Cop ● Military ● Action
http://www.mangago.me/home/mangalist/206/
Honto Yajuu
Any yaoi where the seme or uke is part of the yakuza?