To get the Sakura dog tag you have to have an IP address of Japan . In other words you need to live in Japan. These dog tags they have been release yet .
That's right Sakura dog tags only can be received for players in Japan. My actually location is japan and no player have received this dog tag yet. Maybe in the next monthly patch. No new dog tags or assignments have been release yet
The is not report yet about the Prost one and how to get it . The other ones are super clear how to get them but that want really do not have good information