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.