The M48's with a spare .22LR cylinder are a relative rarity, I believe, in either barrel length. By the time I got around to having a .22LR cylinder fitted (about 1996-7) the factory had no more of the .22LR cylinders, but I got one from Jack First and the factory fitted it.
I've never been sorry. The .22LR accuracy has been quite satisfactory, and the gun keeps that cylinder on almost all the time.
Now, if I could just find a .22LR cylinder for my M53...