A pop up appeared saying collect 15 Candy coin rewards to purchase two new actresses. I collected the candy coins however where or how do you purchase the two new actresses? 

I bet on the "Create a Star!" Quest. To be precise the last part of it, which asks for recruiting 15 actresses and receiving 15 CC.

So you have recruited (instead of purchasing) new actresses with the free slots from academy lessons after you crossed level 60?