Many years ago Marlin made 15 and 25 round "banana" magazines for their model 70HC. If you can find them, those mags should work in your gun as I have gotten the 7- and 10- round mags to work in my model 70. Everything I have read indicates that they are interchangeable. I have never had reliability problems with my Marlin mags.
Those 15 and 25 rounders are VERY hard to find and didn't stand up well to a lot of use, they have a plastic lip and would wear out and not be able to hold ammo. I got lucky and have two 25 and one 15 round, that I use very sparingly. One of the 25's I actually had to glue a piece of paperclip on the lip to strengthen it up (they wear out right where the 22 rim hits the lip).
Although the high capacity is neat, they take forever to load and always seem to be in the way because they stick out the bottom of the gun so far. I have stuck with the 10 round mags for most times when I am using the gun.
Good luck finding some!
