Is there an easy way to locate 99-01 used flatbed duallies or cab/chassis?

 

now you are in to commercial vehicles. finding one will not be as easy as a 350 with a factory bed on it.

maybe try an internet search for "commercial trucks" or "commercial equipment"

you may also have a better chance of finding a 450 or 550 chassis cab as most 350's I have seen have the factory bed on them.