Sounds like a great cause, Wellsley! If you want to look at what charity rides are out there, try reading "Australian Cyclist" magazine. They sell it at newsagents or you get a free subscription if you're a member of Bicycling NSW (which I am)
It's not too interesting if all you're into is DH/FR/NS/DJ, but it's definitely the place to look for charity rides, not to mention mellow MTBing, touring, commuting, and activism. I get it with my membership, so what the hey! AND I'm always commuting by bicycle.