How much have you been trading? You'd have to pretty much be living like a kobold to not hit the human trading requirements in four years, but otherwise you'll have to look through the raws to see if there's anything up. Have you had humans on other fortresses using the same objects file for worldgen?
I've traded 13470 to the tree fondlers and 30998 to the mountainhome.
I've already got the countess and no humans showed up.
The raws are copied over from the Modest mod the only changes I made were adding some more dummy reactions to the dwarfen entity to save moody dwarfs and give the elf a guildrep position I copied from the humans. Oh and I made cartillage heal but this change I made only after worldgen in year 3 or so as my militia commander got his nosal cartillage teared and would die of infection if I hadn't (which is kind of funny as modest mod added healing to many tissues but obviously forgot cartilage ^^).
And I made all of those changes but the elven rep one with the r35 edition of LNP and there everything worked fine.
I've watched in legends and there used to be a human civ near the embark site that got wiped out.
However there is another human civ not tooo far away still rolling.
I mean if the first mentioned civ hadn't been destroyed 170 years ago I would have guessed that there are still five or ten guys hanging out which is enough to keep the civ alive but to few to initiate trading and as you only ever interact with the closest civ of one kind you'd be screwed in this case.
But this way I'm really clueless. I mean everybody showed up the elfses, the goblins, the necros and their undead only the humans don't bother. I mean I'm sitting on dozens of exceptional obsidian doors and thrones and tables here how do they expect me getting rid of all this stuff if I can't trade it for flux and platinum and such?