bro im telling you. autotrader.com. search cadillac sts's and put keyword "sts v" no dashes or anything. Just how I did it. There are so many. Theres even a newly listed 2006 in stealth grey which is pretty rare and will make you a stand out.
There are so many for sale, and just looking at the first couple, they've been viewed a few hundred times, which suggests they've been on sale for more than a day if you know what I mean. Also carguru.com is a pretty good source. theres an 07 with 13k miles for 28 and change on autotrader too. and there are a lot more. You'll have to sift through a few non Vs, but the choices are plentiful. Now go get an STS-V so you can join the family. We're a small family who loves each other very much.