Hello all, I am always getting emails on top Penny

Hello all, I am always getting emails on top Penny stocks that are said to be good ones but i can never figure out where to buy them at? I also know that penny stocks are a waste of time , well that is what i am told not to waste my time with them, I am not looking to become rich with it just maybe some extra cash if it happens. I am a person that holds things maybe to long but i am a Holder, I use this app Robin Hood but most of the time these stocks are not in the search . Is there somewhere else i can look to buy these types of stocks? Thanks