No worries, I found a working remote!
Someone sent me a 49MHz Rebound remote, and it works perfectly on my 49MHz Maxx Traxx, Triple Wheels, and Dagger.
PLEASE NOTE: I have reason to believe that this is only true for the OLD Rebound remote, not the re-release. The re-release used a different internal board, and AFAIK, the newer remotes (post-Mattel maybe?) don't work with the older cars, and vice-versa.