Where could I buy them online, or is there a company and part number that I could make work for a good google search?
Really, i'm interested in 3-4 of these for my own project.
All you need is any relay. There is set of contacts on a relay that turns on or off several other NO(Normally Open) and NC(Normally Closed) contacts on the relay itself, via electromagnetic coil. The NC contacts allow current to flow when there is no power applied to the coil(hence normally closed). When power is applied to the coil, the NC contacts open, prohibiting current to flow, or turning them off if you will. In turn, applying power to the coil also closes the NO contacts and then allows current to flow in them, when they normally would not(hence the normally open). The coil acts like a switch that turns one light off and another on simultaneously. Just wire one light directly to a set of NC contacts, and another to the Coil itself. This way, when the light wired to the coil turns off, the NC contacts will turn on, and so will the other light. When the coil is on, the light wired to the NC contact should shut down. The one wired to the coil must be operated by a timer, but that should be all that you need.
Added: I forgot to mention that for this to work you would have to wire the light, the timer(breaking the circuit and shutting the coil off every 12 hours), and the coil contacts all in series with the output of the ballast. The output of the ballast would also have to be in series with the second light and the NC contacts. Wiring two circuits powered by the same source will not cause problems because only one of the circuits will be operating at any given time, one light or the other. Sorry this was pretty important information, oddly enough I seem to remember things I've forgotten after I get stoned hahaha.
Added again: by any relay I meant any 120 volt AC relay rated to handle your circuits power consumption.