Mt fuji bus tickets from shinfuji/fujinomiya?

Hi I'm planning on climbing mt fuji this summer and have seen the schedule on the Japan guide website. However, I have not been able to find any information on how to buy the bus ticket from shinfuji or fujinomiya to the fifth station. Please help! Thank you.

The bus from Shinjuku bus terminal will reach Kawaguchiko 5th station only.
https://www.highwaybus.com/html/gp/foreign/en/access/index.html

The bus to Fujinomiya 5th station departs from Mishima, Shin-Fuji, Fuji, Fujinomiya stations.
http://www.japan-guide.com/e/e6930.html

According to this page, you can make reservations for the tickets by internet/phone and then purchase them at the ticket counter (at the station) before the bus departure. It seems that you can also purchase tickets at the counter without making reservations first assuming there is space left on the bus

http://transportation.fujikyu.co.jp/english/gettinghere/12.html#pgm03