A2 is available. Same requirement as above. It looks like A2 is the only plot that was released possibly yesterday but I only noticed it just now since there wasn't any announcement. Very weird.
It gets weirder. I didn't have the option to craft any explorer's permit in the exchange, even after I gave some permits away. I ended up expanding to A2 and now I'm fully expanded so I'm pretty sure that there is no other available expansion.