Search for these trains by brand name on the well known auction site. As these companies are Australian based, it is likely sellers will be located in Australia. At that point, you'll need to look through the listings to see who's willing to ship to the states. I just browsed them and found a few who will sell to US buyers.
Ordering foreign equipment from sellers in other countries is not a big deal. I have acquired plenty of foreign models this way myself.
Good luck,
Bob