Unfortunately, using the Armory as a search tool for such a thing isn’t going to really reflect accurate information. For some reason, it doesn’t always update. So just by doing an armory search really won’t help you too much, especially if they’re too low to be registered or just not logged into.
The best ways to go about it? Send the character a letter in game. You can try posting on trade every now and again, appealing to the character or someone who may know of them to see if they’d be interested in working something out.
Another option you’ve got, because the Name Business is a thing, especially on our RP servers? Try here. It’s over two years old, still active and folks will go through and update as they come into names or want to pawn off some they’ve held. You may be able to possibly reach your person there.
https://us.forums.blizzard.com/en/wow/t/wyrmrest-name-archive-redux/94258