I don't know whether you meant the milestone release dates (as in the previous answer) or the actual images. If you meant the latter, they'll all be posted to ubuntu-devel-announce when they're released, and the most recent one or two will be available from cdimage.ubuntu.com. However, we don't keep a full public archive of all the milestone images, so if you're interested in comparing successive milestones then I'd suggest you keep copies of them as we go along.
I don't know whether you meant the milestone release dates (as in the previous answer) or the actual images. If you meant the latter, they'll all be posted to ubuntu-devel-announce when they're released, and the most recent one or two will be available from cdimage.ubuntu.com. However, we don't keep a full public archive of all the milestone images, so if you're interested in comparing successive milestones then I'd suggest you keep copies of them as we go along.
Table for the current and future releases of Ubuntu:
Table of Natty Narwhal milestones: