Mine came from a FWD 2001 Deville. I chose the '01 style, because later years use the newer style Cadillac logo, which doesn't match anything else on the car. You can use later Deville years, though, if you don't mind them not matching.
Yep. Essentially, what you want are caps off of 16" machined finish aluminum Deville wheels, '00-05 models. Some also had 17" wheels, but those centers are a bit bigger and won't fit.
I went with the newer style Revoh mentioned, with the "new" Caddy logo. No, doesn't match any of the other emblems on the car, but it's still the Cadillac emblem and just looked a lot better and more visible than the small etched one on the older versions. All personal choice on what you like better.
Or, as it sounds like you're asking, you can also affix emblems in the centers of the original SS caps like these: