Not sure where you are at, but every manufacturer with five hundred miles of me does gooseneck, with fifth wheel as an option. I just browsed the classifieds, and not a single one listed, aside from a rust bucket out of Abilene, had a Kingpin. Fact is, 90%+ of the haulers up to 5 car, are gooseneck Even if buying new, a Kingpin is seemingly a rare option, somebody new may not have many options sadly.
Not that I endorse gooseneck, it's useful off-road or for applications under 30ft IMO.
Just to give you an example.. I'm out of FL and there are a ton of hotshot car haulers here. It literally seems like everyday (today included) I see a 3 car wedge guy with 1 car all the way up top and nothing at the back of the trailer over the axles. (too lazy to move the last car back or when loading the 1st car too lazy to park it over the axles and move it forward when loading the next.)
With all the weight up high and nothing over the rear axles, it's an accident waiting to happen because they will tip over very easily like that. With as many pictures of flipped-over wedges I see online I just can't imagine these guys are this dumb, but I see it every day...