GContactSync is available, just a little harder to find.
GContactSync is compatible with 3.1 and works well enough for me to import my GMail contacts. I do set it to "Fetch Only" mode though, as automatically adding people I reply to to my address book has caused me headaches in the past.
I wish they'd just bite the bullet and include Lightning into Thunderbird. Lightning for 3.1 is available here: http://ftp.mozilla.org/pub/mozilla.org/calendar/lightning/nightly/latest-comm-1.9.2/ and works fine so far (there are also versions for 3.2 if you're brave enough to be running 3.2). One of my Google calendars wouldn't show up for some reason, so I had to re-add it. The other three worked fine...