You can try one of Marlins resellers. Like low range.
Lowrange is a great source for parts from various manufacturers, prices are usually decent and right now everything is 10% off.
Some things, at least TG stuff I've noticed have shiped directly from TG, I don't know if that's the case with Marlin products. If it is then if Marlin is out lowrange might not have it either, worth checking though.