I believe you are looking for a magazine to hold the cartridges. Midway USA has the proper magazine to fit the model 25. According to the serial number, I believe your rifle was manufactured in 1980. Be sure to specify that date when ordering. Order the old style magazine that also fits the Marlin model 20 or model 80. I have the same model 25 made in 1979, so I know that magazine will work. The link for the page is below. Good Luck.
Drasband, How did you make out? After I messaged you, I ordered another magazine for my Glenfield Model 25 as a spare. I received it on Jan. 12. If you ordered yours, you should have it by now.