where to actually buy a JR regional rail pass before you land

the real sources, not somebody's link from 2019.

1
Start here to see which East regions even have a pass right now, they change these more than you'd expect.
2
some JR East regional passes now sell as an e-ticket straight through this, no mailed exchange order, no counter line.
3
for the Kansai Area Pass and San'in-Okayama pass specifically.
5
Book this before Fukuoka, not after. The airport counter queue in high season is not worth it.
6
redeem the voucher at the Haneda or Narita JR office with your passport, takes maybe 5 minutes.
8
the JR ticket counter at the airport, worst case
If you land with nothing reserved, the JR EAST counter at Narita or Haneda still sells regional passes. Budget 30 min in peak season.

Or start a list of your own — free, it takes a minute.