I'm about to run Oblivion's Edge and there's a part where the players get three Chimeras. I know my players would like to use these to their full extent and I'd like to set up the adventure so that they can. I found stats for the Chimera that someone else had posted but I was hoping to find out which source book that information was from. Thank you!

The stats are postet in "Rites of Battle". Not in the vehicle section directly but in the Imperial Guard Assets. You can obtain a chimera from the Imperial Guard with requisition points, so there are the stats noted. You will have to read the whole text, but I think you will find it.