I recently switched my class from Braver to Hunter but no photon arts(disc) for the hunter class are dropping whatsoever I the class to level 24 and only have one skill that I had purchased from a vendor. Did I forget to do something or...?

It's just the RNG. Your best bet is to buy the others from the Personal Shops, though the prices can be iffy sometimes.

This is why I honestly can't wait until they update the ExCube exchange to have all of the PAs and Techs available at lv17 for 20 ExCubes a piece.