This risks being a useless answer, but the correct method to find references is (drum roll)...

...asking someone who knows more; perhaps by email. Even in the age of MathSciNet, Google, and MO, networking with experts is the way to go. There is someone out there who knows, or knows someone who knows, or gives you a hint to an obscure reference that may or may not have the answer. Plus you get to learn other (un)related math bits and you get to network with very knowledgeable people.

<b>Addendum</b> (in reply to David's comment): My point is that you cannot encode an automated database of mathematical theorems because you do not know how the search query will look like. What happens more often to me is that I find a structure in the setting I study, and notice that some property must hold. When I ask, the answer is something like <i>"That looks like Laramie's quintionic permafrost algebras, but not quite. Your formula is equivalent to Zygyljnski's Platypus Lemma, but the indices are different."</i>

A computer system smart enough to notice that what I describe is related to permafrost algebras would be smart enough to prove theorems of its own. I do not see that coming in the near future.