The easiest thing to do is become a premium member here (it's only $9 for one year, so it's not going to kill you to upgrade) so you can do advanced searches where you can group gear by whatever expansion you're currently adventuring in. Then you click on whatever piece of gear you're interested in, and you'll get sent to the page where you can find out how to get that piece of gear.

Also, don't forget that there are vendor NPC's that sell gear in or near all the cities.It's not great stuff, and it's expensive for what it is, but if you're struggling to find upgrades, that stuff is always there. In the old days, when getting gear upgrades was really, really hard, and before there was a bazaar, those vendors selling leather and chainmail armor and whatever other items that other players would sometimes sell to them, were your only means of obtaining upgrades unless you went hard into trade skills and were cranking out tailored and smithed armor pieces like a factory.