Unless someone lists the specific part number on the message board in a previous thread (FAQs are a good place to check), it's usually easier to find it via an online parts search engine (such as: Rock Auto parts, Tousley/White Bear Lake Ford in MN or Tasca Parts, etc).
Or you could always try contacting your local dealership parts counter person if you have a good rapport with them.
FWIW, here's what I found for your drain plug using Tasca's website:
F75Z-6730-BA
AFAIK, there is no specific parts number search for the message board (but number/letter character strings will return as "hits" via the search feature if someone has previously typed it in a previous thread, etc).
Hope that helps...