Holocaust deniers can simply be pointed to mass graves, concentration camps, photos, etc. Fairy lovers can be asked why it would be logical to believe fairies existed.
You ask for reproducible, empirical data as your evidence, yet humanity has no way of providing empirical data for everything (in actuality, very few things) in the Universe, let alone outside of it, and since the God I believe in transcends this Universe, there is no reason to assume that my God should be detectable/traceable by reproducible, empirical data. The fact that my God is a person further complicates demands for reproducible, empirical data.
Here's a hypothetical situation: Let us say that I am an extremely wealthy, well connected person and you're an average joe whom I have just met outside the coffee shop. We don't exchange names or any other info, but have a conversation about coffee cup lids. You tell the story to a scientist friend of yours and he demands that you provide reproducible, empirical evidence that I exist. You begin your search, but I am in hiding, using my wealth and status to conceal my very existence to anyone who isn't looking for me, or who says they want to find me, but who's desire is only superficial. How would you go about obtaining reproducible, empirical evidence in such a case?