Obsidian Armor

Is there any such thing as collectors that give obsidian armor ?

No, the only "collector" as such is the forgemaster crafter in FoW [must complete 3 quests prior to being able to get crafting done....]

Apart from that, no.

Probably not what you wanted to hear but hope it helps anyway.

For full listings of the materials and costs involved see guild-wiki under obsidian armour [not under FoW armour]