I don't use it personally, but I've several clients over in Israel that use an app called "Whitenote" that allows them to write in Hebrew, which is right to left. Not exactly the same as a "lefty" but maybe it gives you a starting point.
Also, Noteability, Notetaker HD and Notes Plus all three claim to support various layouts for "left-handed" mode. Have you tried any of these? I have all three and find Noteability and Notes Plus pretty much a tie for features.
Pretty much any of the note taking apps that support a "Zoom" function should be lefty-friendly these days. Basically, the zoom box is positional by you, rendering anything under the zoom box a null zone that ignores finger/wrist input. So whether you are a lefty that drags your pen from left to right or hovers over the surface, you should be fine.