My character currently is level 18. Technically, there should be ebony gear popping up everywhere. Smiths selling it and marauders wearing it.

But the best I ever find is Dwarven and Orcish armor. Not to mention those really crappy smiths that no matter how much you level up, still sell mostly iron and steel.

In fact, the game's world has been consistently late in their upgrades in most of my gameplay. I only got a full set of dwarven armor at level 13, but I reckon it should've been possible earlier than that.

Ebony gear doesn't appear before level 32, unless you're using mods that change that:: http://www.uesp.net/wiki/Skyrim:Ebony#Ebony_Armor

That's Skyrim, mate.

So what? You won't find ebony gear before your character is level 32 or so, unless you use mods that change that.

Different game.

I'm not saying this answers all your questions, but the leveled list stuff is a bit complicated -

NPCs cannot carry gear higher than their level. Generic marauders, marauder archers and marauder battlemages are randomly your level minus 1-4 levels. Generally, the best source of ebony armor at your level is from marauder warlords (who are normally set to your level with no offset).

Generally, the higher you go, the more the lower level stuff begins to gradually get replaced by higher level stuff. Even though you can see ebony when UESP wiki says it becomes available, it will be more common as you continue to increase your level.

Venders do indeed sell stuff later than you can begin to find them on foes. And venders will never sell the higher level stuff (like ebony).

More detail is available on UESP wiki. You could start at the link below, then network around the site to put a finer point on things.

http://www.uesp.net/wiki/Oblivion:Leveled_Lists#Items

I figure I'll try every fort, any place where marauders are more commonly found.

I'm at the best level to find Ebony gear according to that link, but I'm sure that the greaves will be the hardest to find just like every armor set.

Ha! Wrong game! Sorry!