This was helpful to me in my most recent search for a vehicle:
https://www.autolist.com/ I also used
https://www.searchtempest.com/ and watched Facebook Marketplace and some of the groups to which I subscribe.
That said, for those of you who prefer the 2003 - 2006 seats, does anyone have problems with the seat foam itself? I can't tell if it is just old foam, or if I need something aftermarket; but the seats I have in my Suburban (2005) and my Silverado (2004) make my backside hurt after an hour or two of seat time). Of course, it could just be my backside is too fat for the seat...