A Captain reports his efforts to get adequate reference data from Maintenance Control to support their deferral of missing brake wear indicator pins on a B737-700.

Narrative

While preflighting the aircraft; my First Officer noticed a broken brake wear pin indicator. This is twice now that I've had one on my aircraft. The first time; there were multiple phone calls; including one to the Chief Pilot at midnight for him to OK the aircraft. I have made many calls to Maintenance Control to be told 'there's a bulletin'; which I have never seen. After rechecking my publications at the Training Center; the Chief Pilot did finally call Maintenance Control and was told; naturally; 'We got a bulletin'. When the Chief Pilot asked to see it; they e-mailed a PDF file of a Request; and a repeat request for Engineering Relief; with no FAA approval stamp and no signature. While I can appreciate that Maintenance might like the relief; I'm still; after months; looking for a piece of paper or a change to the MEL that I can show to an FAA ASI on my jumpseat that says it's legal for me to take the airplane. I have been told that if I wrote it up in the Logbook; they would send a Mechanic out to write 'entered in error' on the right side. The MEL says nothing about brake wear pins; therefore 8 installed; 8 required. I have no other information about how many can be missing from the same wheel; etc. How about we do it right and publish it in the MEL where it belongs.