Update: An official 64-bit build of of Lightning 1.0 beta1 is now available.
Ever since I switched to 64-bit Linux, I’ve been looking around for up-to-date 1.0pre builds of the Lightning calendar extension for my Thunderbird 3 mail client, as Mozilla for some reason does not provide 64-bit builds. For a time I was using a build from zaera-holo.net, but it was never updated and the site now appears to be down. Finally, from a comment on the Lightning AMO page, I found a new build from Friday, which appears to work well. Hope this helps others out as well.
If anyone finds a more regularly-updated channel, please let me know.