To get real potions and spells would be a quick click on the net. You may try if you want to. I am not that foolish anymore. Do you just want to come out and laugh at the wiccans and satanist and tell them otherwise, because they take their faith seriously. And if so maybe you should debate them.
If reading Harry Potter causes children to try to become real witches, we should have some evidence of that by now, since millions have read the books. Show me some statistics, show me some facts. More hits on occult websites is not sufficient; idle curiosity could easily account for that.
Another thing to consider is the short attention span children have. Today's big fad is tomorrow's gatherer of dust. Remember Cabbage Patch dolls? The kids don't.