If you broaden it a little to also include Japanese gardens, then Kyoto is most famous for very nice gardens. You can’t really go wrong. Almost every park, shrine, and temple has meticulously manicured gardens, trees, and plants, even if they are not specifically bonsai-related.
I went to Omiya north of Tokyo, had 1/2 free. You can enter all the gardens (like coop bonsai places). Some of them are more business focused. You should start in the Bonsai museum.
One thing, most place DO NOT allow pictures being taken
After you get out on the train station, you will see maps of Omiya neighborhood with all the gardens and the Museeum. https://www.japan-guide.com/e/e6528.html http://omiyabonsai.jp/