Airsplat carries them.
Edit: I didn't see your post above this. Apparently other people have gotten them from airsplat and didn't have any issues. When you factor in free shipping, I don't think airsplat's price is too bad.
I've been searching through this thread and noticed some people talking about fitting an ambi selector in but I didn't see if anyone actually did it successfully. What stops you from just drilling a hole in the right side of the selector and screwing a lever on the other side? Like this one:
http://www.brownells.com/.aspx/sid=61116/pid=26528/sku/Ambi_Selector_Lever?utm_medium=shoppingengine&utm_source=googlebase&mc_id=10000&cvsfa=2345&cvsfe=2&cvsfhu=3435323030303036392d3435323030303034332d373933