Google is your best friend....
AGT4x4 Manufacturer - AGT4X4 - AGT4X4
Link from the video on Youtube:
You will have to contact them.
I have to admit that they would be handy for some of my shorter friends and parents (I'm 6'3" and my wife is 5'10").
If you are going to inquire...
Point out that you would have to buy them PLUS pay import taxes and shipping to get them to the USA.
Get a price and then see if they would give a discount for group purchase and put out the word with the price and maybe there would be enough people here on the forums interested to make it worthwhile.
One key thing from my point of view...
Being able to 'fix' them with parts from American manufacturers, because I can guarantee they will break down the road. My friend had an Expedition with these and had to have both replaced under warranty (less than 3 years).
EDIT: I sent them an inquiry (via their online form) about price (including shipping and import taxes) OR if they have a distributor in the USA.