G'day,
Welcome to the Forum.
You pose a very interesting question, for which I have no answer.
I'll be very interested in the replies you receive.
I can say that here in Blighty many Toyota dealers won't work on grey imports.
To date, Alphards and Vellfires have not been officially imported into the UK; hence the dealership attitude.
However some, such as mine, will.
I will ask them if they have access to these firmware updates you refer to.
My guess is they won't.
There is Toyota software available, Techstream, that Toyota dealers use.
Whether that contains these firmware updates, or not, needs further investigation.
Techstream is available, on line, and can be downloaded.