You can have as many iTunes accounts as you want. At any one moment in time, the iPad can only be logged into one iTunes account, but you can simply log out of your SA account and into to, say, your US account to download those US apps that you want. Then you can log out of your US account and back into your SA account. Of course, you won't see any pending updates for the apps that you downloaded from the US until you're logged into the US account. So, if you want to check for updates, you'll have to occasionally log into the US account.
I know Members who have four iTunes accounts. For example, in Belgium, the iTunes store has no movies (!) so that Member opened a UK iTunes account and has had no trouble at all downloading movies and apps from the UK store.