After seeing a few of these eBay listings I did a bit of research and made some calls. Here's what I learned:
1. For some reason that's not clear yet, this seems to be mostly a U.S. issue -- dealers in HK, London, and Germany have them readily available, and because of customs issues with lithium batteries, those dealers tend to not ship to the U.S.
2. A Leica rep in the U.S., who I trust, confirmed that more are on their way.
3. Leica has made no reference to discontinuing M240/M10 series batteries.
I'm sure this has been very frustrating for M240/M10 users but it seems this is not the battery apocalypse that many have suggested, and thank goodness for that!