Being from South Africa we are in more or less the same position as those in Australia. If you are willing to use workarounds Fictionwise is an excellent store to buy from - including the restricted books.
I can confirm that using a valid US address and your locally issued CC works for purchasing US only books. Doing the same using acrued Micropay also works. Some books do however require a "geo-restriction" authorization step before you can download them.
Two of the books I bought had this enable and asked for you to verify the info with your CC. All you need to do to skip that, is to use a proxy (
www.hidemyass.com etc.) to log in to your account. The verification notice will be gone and you can download the book like normal. Once you have downloaded it the first time it remains available for download even if you access via a non-US IP.
No CC details are given while using the proxy. It might be a good idea to change your password to a temporary one before you log in through the proxy. Once you have completed the download log out. Visit Fictionwise normally and then change your password back.