Chromium nightly build location
Until recently (last month I would say), you could find the Chromium nightly builds at this address:
http://build.chromium.org/f/chromium/snapshots/
However, it looks like there is nothing there anymore.
Where are Chromium nightly builds now?
The answer you seek is here. You can also find more links on the build page
You can also install the Chrome Canary for Windows and Mac. It's a channel that automatically updates nightly and runs in its own profile.