For this, I bought the Clan Creator Card Bundle add-on, in which you receive SSR cards of Kiryu, Majima, Daigo, Date, Akiyama and Saejima. Once you do the first clan creator mission, you are then able to organise your clan by speaking to Masao, and then use the SSR cards you received and the achievement will pop.
Another method is using Clan Codes and get a bunch of special leaders that are SR, R and C cards. To use Clan Codes, once again, simply speak to Masao at either La Pente or the M Side Cafe and you will get asked if you would like to enter the codes.
This guide by CyricZ on GameFAQs has every single code you will need.