for food service use Taylor Co. make what is known as Taylor Lube, this is a food service grade vegetable grease.
If your LHBS doesn't carry it look at a food service or restaurant supply company. Many of the have a "will call" desk so you could get it cash and carry.
I use this on the keg gaskets. Using forward sealing faucets (i.e. Perlick or Ventamatic) and cleaning my lines with every keg change I have yet to lube or have a sticky faucet. An overnight soak in PBW also does magic to clean up the goop that builds up in the dispensing chamber.
