I was able to get them on my 2017 355MBQS from the factory. Other who ordered within the same timeframe were not. I don't have the invoice here in front of me but in round number they were about 1000$ for the four slides. My dealer commented when we got the order confirmed and pricing that it was much cheaper than he expected or could do it for.
Your best bet when you order is to have your dealer get his Jayco rep involved.
My dealer was not aware that this option was available, he went on my information from posts here on the forum and has now since started ordering his stock units with them as well. He thanked me for filling him in.
The other perk of getting them from the factory is they are covered with the two year warrnaty.
2009 F350 CC LB 4WD
2017 Jayco 355MBQS