I don't think it's a matter of who will insure a non profit, I think it's a matter of who will insure them for Civil Rights violations. Those are not accidental acts, and would anyone actualy provide coverage for that? isn't that your real question?
You can buy coverage for Tenant Discrimination, perhaps you should talk to an E & O broker and see what they have to offer.
"It's a typical day, on the road to Utopia.."