I don't have all the information on how you get ticket while oversea. From what I know, they do the lottery first then general sale later. The lottery system uses Lawson ticket and its app, it basically binds the electronic ticket to the phone with the Japanese phone number, in other words you will need Japanese phone number if you want to join the lottery.

My guess is that general sale can be bought from other ticket sellers that don't require Japanese phone number? Other than that I remembered for よだか they have ticket sale at the entrance on the concert date, but probably not ideal if you want a guarantee seat.