Is there anything particularly wrong with using vaseline as beer gun lube? I just serviced a second hand beer gun (now I have two :icon_chickcheers: ) and quick-disconnect with it as I don't feel like making yet another trip to the LHBS.
You can also go to any dive shop and get a little tub of the silicone grease they use to service dive gear. Food grade, not petroleum based and a tub lasts forever.