How to find references for known facts? It occurs sometimes that I am in possession of a factoid for which I know all of the standard terminology and can express the factoid in that terminology, and also know that the factoid is prior knowledge, but do not have a reference for the factoid.  This is especially problematic in my field (machine learning) where the online resources for learning things are very good, and quite extensive.  However, citations are sometimes sparse in these blog-style articles, and I find myself knowing the subject matter, but not knowing the appropriate citation for it.  Note that the blog is not the appropriate citation, because they're just paraphrasing it from elsewhere.  It would be nice to lean on the experience of the community, but "Does anybody know a citation for fact X?" is generally an inappropriate question on stack exchange sites.

Surely this is a problem in other disciplines as well.  As such, I am mostly interested in general "citation reverse-search" skills, tips and tricks.  However, field-specific answers are also welcome.

NOTE:  This is specifically for situations where the problem is known to be a prior one, and where the terminology is known.  Linking disparate fields with differing terminology of basically the same concept is a known Hard Problem™, and I am not trying to solve it here, except insomuch as those same skills relate to "reverse-search" of problems with known terminology.

To reiterate for clarity:  What are handy tools, tricks tips etc for finding 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 :)