I'm afraid I have little advice to add here. Bill Garrett clearly offers the best solution. My impression is that CMRRA offers licences for recordings released in Canada, and they only offer licences on behalf of publishers they represent, which means in many cases you have to go directly to the rights holder. For a US release, Harry Fox is the equivalent even if the rights owner is not American. If the song is not on Harry Fox's radar, you're back to the direct approach. It's often a royal pain.