Google Bard is trained on a totally unique software system that was forked from the original google search process which was built on Python, but that came originally from Freebase which was built on Graphd and MQL - both of which are 100% open source and available to work with, hell even Python is available. But, you'd need the original source code for Freebase which is openly available on GitHub.

So, you're welcome to grab all of Freebase and start a sandbox, but good luck getting it to anywhere near a trainable AI chatbot. Freebase is the starting code for everything from Ring doorbells to the DMVs back end.

A good comparison would be sitting back and looking at a mansion on a hill and thinking, hey, we should build our own mansion on the hill, all we need is the supplies. Then, your friend comes along and gives you a bucket of screws and says good luck and walks away. You don't even have a screwdriver, let alone a piece of wood to screw them into. You're so many steps away from the mansion that you'd be better off just dumping out the screws and sitting on the empty bucket.