Not physically possible...
If you're talking about a 25 round mag, it's not possible to make a straight mag. The very fact that the .22LR has a prodruding rim, by necessity, makes the mag have to curve.
Stack seveal .22 rounds on a table and see what happens. In order to make them straight they'd have to have a space between each at the front the same as the thickness of the protruding rim.
Staight mags are often seen for 9mm and .45 because the rounds have perfectly parallel sides.
I'm sure if you come up with a way to make a working 25 round straight .22LR mag, you'll make a fortune.
BB.