You can actually find trash cans but the one (and only) time i went to Japan i found the trash cans typically at parks, nature/hiking trails, etc. Occasionally it was still possible to find them in other spots, by train stations, bathrooms and other similar types of hubs but honestly i just mentally prepared myself for not having access to a trash can and i stashed everything in my backpack. I typically don’t snack, drink soda, etc so i don’t make a lot trash when i’m out and a about so it was never much of a concern when i visited the country 
