Sanyo Shinkansen 1-way discount ticket

I am a US passport holder residing in US, visiting west Japan Oct 11, 2022. Buying a Kansai Wide Area 5 day Pass to visit Nachi Falls. Then plan to go from Osaka to Beppu. Where and how can I buy a Sanyo-shinkansen one-way discount ticket for foreigners for 10,500 yen in US or online? Please advise, thanks.

https://www.westjr.co.jp/global/en/ticket/pass/one_way/#sanyo
Scroll down to the section that says Purchasing a "Discounted One-way Ticket"
Sounds like the kind of product you could get from JTB/NTA/HIS.
It will get you to Hakata, not all the way to Beppu.

Options I think of is; to hop and search Kinken shops in Osaka (discount ticket or share holder's discount cert), travel agencies, discount flight ticket, ferry ride from Osaka to Beppu. Ferry is normally the least expensive.

KyushuLocal, please note the website states
The "Discounted One-way Ticket" is not available for purchase within Japan