These updates have appeared in the Mac App Store for those who purchased the apps there originally. If you purchased them via iLife ’11 on Disc you’ll have to wait a bit longer until the updates appear through Software Update. You can find GarageBand 6.0.4, iPhoto 9.1.5, and iMovie 9.0.4 in the Mac App Store, for $14.99 each. Update: now available via Software Update.
Apple has now made the updates available via Software Update: