I think Andy should focus on catching either a Water-type or an Electric-type next, although probably the previous first, since they're both common, and counter Belladona's weakness's, while Elect- Ooh, I've just realised an Electric-type would be more useful, covering both Zephyr's and Molotov's. Ahh well, I guess it doesn't really matter, but I do plan on catching something in that typing. Hey, if I find a Chinchou...
And I'm pretty sure you can find Rhyhorn in the Hoenn Safari zone, I'll check Bulbapedia in a mo', and I'll use that to see what kinds of Water/Electric types you can find in Hoenn, since it's not my most well known region.
EDIT: Yup, Rhyhorn can be found in the Safari zone, and my eligable Water-types would be Walrein, Kingdra on Lanturn... probably... I'll just go on the spur of the moment.