The challenge with finding a 2015 to 2017 K900 V8, Luxury or Luxury VIP, is that there were less than a total of 1,600 imported to the entire United States. Unlike what the buyer leaning market for end of year sales on a new 2019 K900, the used car market is seller focused with a horde value seeking buyers chasing a limited number of vehicles, IMO.
When KMA brought the K900 back in 2019, from its 2018 hiatus, as I understand it they adjusted the importation to only be cars ordered by dealers, nothing in reserve by KMA so it constrained availability and slowed delivery in the beginning of the model year. It forced dealers to estimate what they could sell somewhat before they could assess the market and probably cost them some sales early on. Now at the tail end of that model year, finding a new 2019, most likely in the midwest as sales are strongest on the west and east coasts, is still possible though that opportunity is slowly slipping away.