Potty chair with tray
I'm good at searching, so I thought I'd give this a try. I'm actually surprised that this isn't really a thing in the world. The only thing I could find that comes close is this:
It's usually posted as a joke for the reviews, but as the actual product goes, I don't think you HAVE to put an iPad on it, and if you don't, maybe the tray is just a flat surface. If a potty chair with a tray is what you want, this might be your closest shot.