I have an older Marlin 60. The inner magazine tube is 20 7/8 in. from metal end to metal end. The outer tube has the split at the end for the pin on the inner tube to engage and lock. My original owners manual list the outer tube as P/N 307423. Anyone know where I can get a replacement for this outer tube? Everyone I find is too short. Marlin's web site says they don't support this model due to its age. Thanks for any help.