How do I find a replacement Seat Post Binder screw for CAAD8
The thread is almost certainly M5x0.8, which is the most common small fastener size on bikes, and common on many other things. Any bike shop and fastener/industrial supply stores as well as any hardware store with metric bolts should have it. Seatpost clamps usually take a hex cap bolt but they different in what length they need and sometimes are particular about the fit of the shoulder. The simple thing in your position would be to use a flat screwdriver or a pick to work the snapped bolt out and just bring the rest of the clamp in when you go get a new one.

Model year type data for something like this isn't really how it's done on bikes.