I just encountered one for the first time a few days ago in the ruins where you retrieve Jurgen's horn. I was like WTF is this! I've played so many hours and this is the first one I've encountered.
What level were you on? Hulking druagr are rather rare anyway, even for high levels. But they do show up. I have seen several. Hillgrund's tomb, Korvanjund, volunruud, soljund's sinkhole maybe dustman's cairn, and maybe
vathume. Also possibly during the dawn guard quest line, I don't quite remember where though. I seen them on solsthiem too, but I forgot the places names.