Dwemer artifacts could be acceptable. Perhaps the skyrim area could have dwemer ruins or some other indiginous miner race creating crude and bulky technology as steam and available magics combined to power and drive their homes. These places could harbor a firearm or two.
Innitially I was opposed to having guns in the next tes game but, I remembered my time in morrowind. There were instances when I thought a blunderbuss or flintlock would fit the location.
I've already explained that the only instance a somewhat crude "gun" appeared was because it came from a robotic centurion, which would only work on said centurion because the robot as a whole could produce enough pressure to fire the darts from its arm single arm. I'd be worthless, other than clubbing someone with it, if you ran around with the arm of that dwemer robot. Plus, no one has even come close, except for Sotha Sil, to be at the level of dwemer tech. Not even Dyviath Fyr, who has a bit of an obsession with dwemer and has lived since 200 years after the first year of the first age (in otherwords, he's almost lived through ALL of history after the Mythic Era), has come close to creating his own dwemer tech. And Sotha Sil wasn't even concerned about making weaponry in the first place. His whole obsession was his clockwork city, which at best for weapons housed some robots and mechanical abominations.
And like I pointed out earlier, it took 3000 years since the beginning of the first age to move from armor made out of hides and leather to metallic armor. Pelinal and the dwemer armor were considered to be highly futuristic during their time, and it's only been the last 1000 years since armor like theirs has been somewhat reproducible, without the aid of daedra.