Anon, or Josh, volunteered his time as an on-site cartographer to help create the maps and modes which went live in the Action Sack playlist with the Monitor's Bounty update. Since then, he's put the scripting knowledge he gained there to work recreating classic game modes.
Rocket Race is one of the three modes AnonFriction has recreated so far
To bookmark the mode prefabs themselves or the Arena maps they're set up on, Josh's file share can be found here. He has also compiled all of the info on the modes into a thread here. Be sure to keep an eye on the thread for future game mode releases as well. The next one will be very important, people!