Pathfinder's City of Lost Omens set featured the Wave Rider mini who had a hippocampus as a mount. I believe the only other hippocampus minis I've seen have been couple of Reaper brand miniatures.
I think there is a Hippocampus in PFB Cities of Lost Omens, with a Sea Elf rider. But yeah, we need a more easily available Uncommon Hippocampus. Theros has stats and art for one! Nice comparisons, and here I thought the Exandria Gorgon was an oversized super-Gorgon, this is quite huge too! Funny to see how different sized the old Icons minis are, like that Gryphon or the ToD Harpy.