The other place old classics go.
Pat I think your right about a small percentage of the lux-O-barges, but I suspect a large number of them just ended up cut up for scrap/chrushed when they fell out of style.
I remember several years ago helping a friend of mine getting ready to do his annual crushing. We sent out 3 complete, straight, rust free early 60's Buick 2dr Hardtops. It seemed a total shame and I mentioned this to him. His reply was that it was a shame, but they had sat there for years, and in that time he had not sold a single part off them (let alone anyone having come in interested in the whole car). It was time for them to go as he needed space for the "new" cars he was hauling in.
With the fewer numbers of luxury car produced and an extremely small demand for their parts finding one to even start building will be a challenge.