All the details of the design and how it works are available in my little electronic projects GitHub repo (it is basically my open lab notebook, with a catalog of over 400 projects now).

Here's a quick demo of the contraption in action:

I am somewhat cheekily entering this in the MacroFab LED blinky competition - mainly to spread some Boldport luv. While you can obtain the parts from Mouser, and fab the board based on Boldport's open-source design, the easiest way is really to be a Boldport member and get the kit direct from their store.