After consulting my Japanese street slang dictionary, I've gotten;
zoku- meaning tribe or gang, and can be used as a suffix to create a new slang word for a new kind of tribe or gang, it is widely used in Japan.
chinchin- a cute word that denotes the penis
To call a group in effect; a dingaling gang, you would say- chinchinzoku.
You could also just shorten it to chinzoku. This would make sense if all your assassins were very unassuming and good looking innocent types.
Bear in mind that chin-zoku is a term for a family that eats meals prepared in a microwave oven. I believe there is a syllabic stress difference in chinzoku and chin-zoku.
Other possible prefixes to zoku-
Chonga- meaning bachelor
Dani- meaning a lecherous member of society
Hayai- meaning quick, applies to the speed of work done, Te ga hayai translates to "the hands are quick", but is slang for "fast worker" or "sexpert"
Of actual killing-
Yaru- meaning to do in, slang for to kill
More words implicative of kill-
Korosu- the standard word for killing or murdering
Koroshiya- meaning hired killer
Satsugai- meaning slaying
Satsu- meaning the character of the korosu, or murderer
Bukkorosu- meaning totally kill
Bu is a prefix used as an exaggerative element resulting in a fiercer adjectival slang word