I have a Micro Matic regulator # 3499

that needs the diaphragm replaced - I think that's all that's wrong with it. Where/how can I acquire parts. Secondly, I want to pressurize kegged home-brewed wine with Nitrogen and have found a source. Can a 3499 be used for Nitrogen, and if so, how can I acquire the proper nipple for connection to the tank (or an adapter that will accomplish this)?
Finally, do you have any specific advice for establishing such a system - I assume the standard beer connections and equipment will be appropriate? I'm using pin-lock devices. Is there anything I should be concerned about with regard to the relative molecule sizes of N2 and CO2?
Brian