There is lottery rounds for both fanclubs and also one for the public (but you need to be registered to the ticket site afaik).
First was the lottery for members of both fanclubs, then for Koda Gumi, her main one, and right now it's for the KK app till February 25th. Having those three rounds isn't new, it's been like that for some years now (I think it started 2017 with the double member round? Back then with Koda Gumi and playroom ofc).
But indeed it's not made for international fans, but sadly that was to be expected with them closing down the international Koda Gumi.
The presale round for the public is March 2nd till March 6th (usually through the Lawson online site, but they haven't said yet).
General sale for the rest of the tickets then starts March 30th.
You can buy tickets from the general sale on the machines in Lawson stores, that might be an option being in Japan as well (as you said).
You find the info of the sale periods here:
https://rhythmzone.net/koda/news/detail.php?id=1114084
They make announcements in the news section on her official site with the start of every round, so best to check the site regularly.
Some dates might not be available if they sell out through either of those rounds.
And if dates don't sell out, they also sold tickets at the venues in the past. But sometimes to a higher price and those seats are always in the back.
Tickets are also digital this time, so you need the Anypass app, which does work internationally.
(every person going with you needs a ticket through the app btw.)
Good luck, I seriously hope you will be able to snatch some tickets!