Neither have I, but most officers, at least those Captain and above, plus Academy graduates, both own and wear them. Usually at least a couple of times a year, as far as I can tell.
Heck they have so called Dining Ins and Dining Outs (which started out as Wing Dings during WW-II in England and grew out of similar RAF affairs), just so they can wear them. Then there is often a Military Ball, and a Christmas affair of some sort. But Reservists don't have all that stuff, maybe a Military Ball and/or a Christmas dance depending on location.
"Reservists don't have all that stuff" - hmmm. I'm a reserve JAG O-6 and have had to wear my mess dress a couple times a year for the last 6 years (since I was an O-4). Maybe not in the unit world (although part of my time was as an SJA in a flying unit).