Try e-gunparts.com
A Marlin Model 60 is a very popular rifle. To find an inner magazine tube for this firearm, you can turn to your local gun dealer. There are also a variety of online resources available that will offer this piece for sale.
You can purchase a replacement 7 round magazine from Numrich Arms at www.e-gunparts.com. The Part Number is 403080B Cost is $19.95. It is the same magazine used in the Marlin 80 Bolt Action rifle. Happy shooting!
Good luck. Every site on the Internet seems to be out of the 10 1/2 inch magazine tube for the Glenfield/Marlin 75. Keep in mind, the Marlin 99M1 uses the same tube, but that is just as hard to find. I have been reading up on converting it over to a Marlin 60CC Magazine Tube inner and outter, but not even sure that will work.
www.gunsamerica should be able to help
www.midwayusa.com
Try e-gunparts.com and Marlin
go to sears pick up a magazine and wow u have a sears magazine
Brownells has replacement stocks for the model 60. You can also go direct to fiberforce to get one.
Try e-gunparts.com, gun shops, gun shows, internet
I would start my search at Numrich gun parts corp.
Best bet would be to write to Marlin and ask them. They pay attention. You can find their address at www.marlinfirearms.com .
Sadly, your rifle has been out of production for a LONG time. You can check with Marlin thru their website, or have a gunsmith check his sources for used parts.