The only place I know of currently selling a K790a is Amazon.com.
If you find a website that says it is selling the K790a, double check the bands, it should be 850/1800/1900mhz. If it isn't, then the person selling it, made a mistake and is selling a K790i or K800.
Where can I purchase this phone?
It's been out for a long time already. The SE website also shows that this phone is released, but no one is selling it. Only the SE K790i, whose use is limited here in North America.
Anyone has any clue where to get this phone? And what do you think the price will be?