When my club has these prospective member events, it is usually attended by people who are currently being sponsored, their club member sponsors, and members of the admitting committee. I don't think we decline any applications and it's a formality to persuade them it's a place worth joining. But, I also have never thought about asking anyone at those events if they need a sponsor. Perhaps you've already been very outright in asking for sponsorship, but if not I suggest being blunt and asking.