From the menu, choose the Password option. Enter the password, and then a swarm of that Pokemon type will show up the next month.

Effect	Password
Keiji Special Mission	EDw8w2HaRn
Motonari & Motochika	J2TRZXPUm3
Okuni Special Mission	gauRnak2nR
Ranmaru Special Mission	2aL38Ek2Rx
Reshiram Event	2rz3XFEKxR