Tickets for a NPB game!!1

Hello!! I am exploring getting NPB tickets for my last evening in Japan on my upcoming trip, and the Swallows and Marines are in town for their home openers!!! Now that Japanball is gone (thanks Giants) what is the best way to get tickets at face value if possible? Preferably the Swallows but I am open to traveling out to the Marines (their stadium area on the water looks quite nice). Any help is appreciated. Thanks!!