I've seen plenty of resin balls at the store and cursed a leaking Harry Potter one myself.
Meanwhile I'm experimenting with using acrylic paint varnish for the liquid as the one thing I did try to make with their resin did not cure after spending hours in the sun.
PS: If you look on Reddit you can find how to read pin hole marks and codes on MGA balls to figure out what's inside. So far it's been working.