I mean, it's been out for over a week now. What gives?

Sure, you can find the list, but why isn't it in any of the achievement tracker sites?

Basically, it's all a load of challenges, with a few exceptions:

kill final boss, finish on easy/hard/commando, collect everything, s rank everything.

info?
http://www.xbox360achievements.org/game/bionic-commando/achievements/

Look at the forums on that one. they always make the achievement guides there:
http://www.xbox360achievements.org/forum/forumdisplay.php?f=853

It's not appearing on xbox.com, meaning achievement sites can't pull the data from the microsoft API

Yeah xbox360achievements.org is my go-to place, they must have just added it.