apparently no stores around me have direct fit batteries listed 
I recall when I was looking for the proper replacement batteries for Prius, I found on priuschat.com that people were using some marine type of battery with the hydrgen vent tube port present, but it was needed to bolt connections directly, not using the original clamps, it was enough space to fit it inside. I ended up using the purpose-built non-OEM battry and it works great so far
I bet you could use anything what has the vent port and more or less fits the space, in the end it is not a cranking battery, so some difference in capacity will not do much difference
it is also OEM route, but it’s too lame 