I’ve had several in dungeons. I’ve been somewhat lucky in coming across them, I came upon three, one right after another in Hawezar one time but got zero good drops.
Also have been fortunate enough to not have another player come across and kill any of mine prematurely, although I did lose one once when my slow as heck Druid got bogged in a big pack that it just blazed through and I couldn’t get through and had pretty much everything on CD at the time.