Is there a listing somehwere that tells you how to get all of the old Tier and PvP gear for pure transmog purposes? I am horribly confused. I think some can be purchased for Valor Points but there seem to be several vendors throughout the world. Some you can only get from Darkmoon I think? And some you just have to solo old instances, get the old tokens, find the old vendors, and get them that way.
Is there a clear list or wiki that says 'for tier X you have to go to Y vendor'?
Most old instances have their own tier or a tier shared between them. Many of them drop tokens which yes, are all over the place so a simple guide would be good for that. Off the top of my head: TBC gear is sold in the Scryers/Aldor main building and from the Naaru behind A'dal and I think on Isle of Quel'Danas as well. Wrath gear is sold from vendors in the Sunreavers/Silver Covenant areas and also outside the instance for ToGC. Cata gear is sold from vendors above the throne room in Org or in the building near the stables in SW, and also inside the instance in FL. MoP gear is from the vendors in Townlong Steppes, the Shado-Pan area in IoT (this VP gear is still relevant BTW) and the vendors in the upper area of Shrine. I've probably missed a few there...
Also yes, there are vendors in DMF which sell old gear lookalikes for tokens. Also there's one in Netherstorm that sells old PVP sets I think? But you might have to have earned those back in the day. Also old PVP gear is available in the big PVP hut in Org/same building as Cata gear in SW.
I recommend getting Atlasloot if you don't already have it, shows you everything that drops pretty much everywhere. And if you're unsure where it drops you can then look it up on wowhead or whatever.
Don't forget there's also:
-Old crafted gear
-Random world drop greens/blues/even purples, some of these have very nice matching sets
-Old quest reward gear, sometimes these have unique skins