Here's two I really like:
http://www.mangago.me/read-manga/hana_to_ryuu/
http://www.mangago.me/read-manga/saezuru_tori_wa_habatakanai/
I love this manga too: Bi no Isu (Prequel) and Kobi no Kyoujin (Sequel): 1. http://www.mangago.me/read-manga/bi_no_isu/
2. http://www.mangago.me/read-manga/kobi_no_kyoujin/ ... (โงโโฆ)
here's my list of yakuza men doing actual yakuza work http://www.mangago.me/home/mangalist/43239/ you can look around, i've labeled everything up
I'm looking for yaoi mangas that include yakuza, mafia, drug dealing..etc like finder