How to find references for known facts?
Actually, there are often many "facts" that really aren't. It is a fascinating research question to dive into the internet and libraries to verify the origin of something taken as a fact. This happens in every field and especially with pithy "quotations" that appear on calendars. Just for fun I like to look for the true source, in one instance I came up with five different supposed authors! This is also why you should reference your facts: So that others can verify that you are stating it correctly. 

In the area of machine learning you can use the ACM or the IEEE digital library to dig around and look for a source. There are no shortcuts, this is research :)