[Searching for Natu]

You can catch wild Xatu in Victory Road (Amethyst area) and breed to get a Natu.

[Stuck in Rhodochrine Jungle]

Spoiler

I got stuck here for a while, too. You can progress the story by falling through one of the holes or going through one of the caves to get to the underground area.  Then navigate to the bottom right area of the underground to find a cave exit. Going through that and exploring the new area will progress the story.

 

[E17 Obtainable Pokemon List Changes [Potential Spoilers?]]

Weedle was changed to "evolution only", I think.