Hi Oz. Please don't get me wrong, i am not in any way "knocking" older music but what i am saying this that socially, outside the scope of ballroom dance events, you are much more likely to encounter more contemporary or modern music. In addition, in order to attract a younger audience to ballroom dancing and keep it alive, playing modern music which they can recognise is much more likely to attract their interest.
I dance and listen to a great deal of older music but bmaniaci's resource is very useful for finding new tunes.