Randall is correct, the speed sensor is built into the bearing/hub, just like the fronts are. It is not a separate serviceable part, and to replace the speed sensor you have to replace the hub. If you go that route, I suggest Timken bearings, and rockauto.com probably has the best prices. We have a write up on the forum showing an easy way to get the old hub out if it is stuck in place and won't come out. Let me know if you need it and I will dig it up for you.
I also suggest replacing both sides, not just the right. If one failed, the other is not too far behind.
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)