Check your yellow pages or online for your local beverage distributor. Not sure if they would be able to sell you just a pallet, but it couldn't hurt to ask.
If that doesn't work, do you have a local warehouse club in your area like Sam's Club, Costco or BJ's? Give them a call. One of your church members will likely have a membership card if you don't or maybe if the church plans on buying items in bulk they will have a membership or would benefit from getting one.
If neither of those options are viable for you, you could try contacting the manager of your local grocery store and see if they would order extra for you when they make their order from their warehouse or distributer.