We are a private school and do an annual auction and have obtained great responses for donations! We have received a few that indicate that they don't donate to religious places, but for the most part those are few and far between.
I don't have the list any longer.....I basically sent a letter to everyone on the list, excluding ppl innappropriate for elementary schools. So my suggestion is just track this thread and create your own lists, including those that say no to us might say yes to you...who knows.