I have, by both accident and design.
Traded the accidental ones, until I picked up a BAR mag with some M-14 mags.
Used to be, back when I had a job and money, one of the things I'd shop for at gun shows was odd-ball mags. If the price was right, I'd pick up a couple, or some such. Which would go into my for-the-gun how "possibles" bag. Can be handy to have found a deal on Sterling mags to "sweeten" a deal on 1928 Tommy stick mags.
Never found a deal on an L mag to stick in the drum carrier bag I have. My three-cell & 5-cell tommy mag pouches are good to go; as in the '43 dated BAR belt I have. I need to find another 5-cell bag for my M-3 mags (except that having them in a universal pouch is equally accurate).
So, in my perfect world, I'd need a BAR, an M-1928, an M1A1, and an M3--and seeing as how I want to get back to having a Garand and an M1A . . .