Just a quick update:
Toys'R'Us Whampoa is closing down on the 20th September 2020. Whilst it was a smallish store because it was "out of the way" it often had limited numbers of rare/exclusive stuff a little longer than the main stores. It looks like Toys'R'Us are focussing their efforts on their flagship store in Tsim Sha Tsui (TST).

On the positive side, Cathay Pacific have just announced they are now allowed to put air mail in the cabin for their HK - AU flights which may mean HK Post has allowed air mail to be sent once again and opens up options to use the HK stores that sell online (eg Robot Kingdom) although I would strongly encourage you to check with individual stores on the postal situation before purchasing for now.