Where can I get 'classic' Lego heads from?
The well known, smiling, gender-neutral multifigure head can be bought on auction sites like Bricklink. 

The classic faces are still in production now and are on the minifig or every set in the modular series. (The Grand Emporium alone has seven of these heads) As well as other modern classics like the carousel, winter toy shop and town plan.

Up to five of these heads can be found in most editions of the Vintage Minifigure Collection.