Two things,
Mr. Pibb zero is available at the Coca-cola Marketplace, it's the only place I've seen it, and its the best drink I've ever had.
Also, I have purchased a drink in the park in quite some time. Does the park still not carbonate the Orange Fanta? I remember when I had a refill cup some years ago the Fanta was always just the juice. It was the weirdest thing and it was like that everywhere, but I really liked it.