Where can I ask for specific statistical data?
Nowhere. Not in Stack Exchange for sure, and probably not any forum or Q&A site.
Stack Exchange sites have clear scope and focus, which by itself can't be too broad. For example, there is no SE site just for books as it would be too broad, but question about Science Fiction or Fantasy books can be asked in Science Fiction & Fantasy site, and question about cooking books can be asked in Seasoned Advice site.
Taking your example, "How many books are published in the Irish language every year?" needs research in several areas of expertise:
So no Q&A site or forum is likely to accept it. (As long as it's not "Ask Me Anything" kind of forum)