For our planned June 2020
ABD Japan trip, I bought a Tokyo Disney Resort package on my own to append to that trip. I did that six months in advance at this site:
https://reserve.tokyodisneyresort.jp/en/hotel/search/ It accepted the same Disney account (email and password) that I use in the US.
I used a Visa credit card and had no problems getting that accepted. I did call my bank in advance since the site warned the credit card needs to participate in the "Verified by Visa" program but I didn't have to do anything special in advance.
The package I bought had two nights at the Miracosta but park tickets for 3 full days. So I booked an additional night at the Hilton Tokyo Bay, which is on the monorail line. That way we could make full use of the park tickets. The package also came with Fastpasses, drink coupons, monorail passes, two breakfasts (which had to be scheduled when you bought the package), and a popcorn bucket.
You would need to handle the transportation yourself. I was planning on taking a taxi from the Peninsula to the Tokyo Disney Resort, asking the guides or the hotel for help with that. It is possible to use subways/trains instead but that would be annoying while carrying a bunch of luggage. You must pick up the package at the Tokyo Disney Resort Welcome Center (close to the JR Maihama station) prior to going to your hotel. To get from the hotel to the airport, buy tickets in advance for the Airport Limousine Bus which runs from your hotel to either Narita or Haneda airport.
Of course, the ABD trip was cancelled. I had no problems cancelling my Tokyo Disney Resort package and received a full refund.
I don't know what the situation is today in terms of buying these packages, or if they are even allowing international guests to reserve these.