Despite all of the hand-wringing, wailing at the walls, sturm & drang, etc., I can go to just about any of the 2 rail meets/shows and fill the back of my Outback with cars and engines any time I want - there's no shortage of available stuff in O scale, but there is an overabundance of myths.
I remember one show where someone was selling 2-rail freight cars, most with metal wheelsets and KD couplers for $8.00 apiece. I bought a few that I liked and when I got to my car, I realized "What a fool I was, what a.....", promptly went back and bought all but one or two of what was left. I did fill the trunk of my car; all for less than a hundred bucks.
Can't buy trucks and couplers for $8 a set. Cars may be rubbish, but hard to beat the salvage value there.