I read the wiki, and supposedly once I am an apprentice in destruction, they should be in the possession of two College of Winterhold teachers and the court wizard of Whiterun to sell. However, they won't appear (save unenchanted apprentice hoods).

as you level up the general store merchants will have em...also radiant ramient hs a big supply..forget the apprentice robes,,,you can find robes equivelent to that,,save your money and wait till expert or master robes are available.