Part of the scholarly base is your network of scholarly contacts, people who can give you advice about your research. Recently, I finished a chapter and sent it to someone I had been in correspondence with a few years ago. He responded with some comments 24 hours later. This person is a poet and linguist, and more specifically is one of the leading linguists specializing in the prosody of Spanish. What incredible luck. When I was writing Apocryphal Lorca I had access to Jack Spicer's biographer (Kevin Killian), to Kenneth Koch's editorial assistant (Jordan Davis), an expert on Creeley (Ben Friedlander). To several Lorquistas. Pretty much everyone was willing to help, whether they were people who happened to be my friends already, contacts I had cultivated over the years, or simply people I contacted out of the blue. The key is approaching people respectfully and asking intelligent questions. The consultant is not there to do your research for you, but to tell you if you are on the right track, or sometimes to save you from dumb errors of fact. You wouldn't use a leading scholar to be your copy-editor (unless you are close friends and read each other's work).
This seems remarkably easy, but the problem is that you have to have the confidence to contact people, and you have to be at a certain level already to know what the right questions are to ask. I wouldn't email a leading physicist to explain string theory to me. For certain dumber questions you can ask people in your own university you know.