You also get them back from deconstructing nirnhoned items that drop in the wild, but there is no 100% guarantee. Those are meant to be used for trait research more than anything. This also applies to the one's you find in guild traders. Most of them are made to be used as training mats and not decon mats. You will rarely find them made in specific craftable sets and usually for a ton of gold
If you are planning to use the nirnhoned gear for research, DO NOT decon it. Instead, craft the item you want to research and then transmute that. It removes the chance of having a loss of crux from deconning the item if you plan to just make a different piece for your toons. Just something I learned while doing trait rese4arch for my alts.