So I ended up ordering the Motobecane Boris LTD from BikesDirect. They just got them in stock (it's shipped but I don't have it yet.) $899, seems like a decent bike and comes in XS frame size.
I spent a few months combing through craigslist, FB marketplace, pinkbike, etc but with the combination of needing a less common size, low popularity of fatbikes in my area, and the bike shortage making everyone massively overprice their used bikes, it wasn't looking promising for finding one used.