Book Business, for example, gives a list of third party operators, which manage cultural attractions and park services. Books that provide educational value and fit the niche can be selected.
Bigger stores, such as Costco and Walmart, are harder to get into. New Shelves writes that they have limited shelf space, and books need to have a proven track record before being considered.
If you are trying to sell your book in a store, you will probably need to do an offset printing, instead of print on demand. Self Publishing Review explains the differences and the pros and cons. Typically, offset printing results in books that look higher quality, but you do have to store the books somewhere, and you will have to pay upfront.
One other thing to consider is creating a large print version of your book. Andrew Knighton wrote a how to on making large print books, which includes leaving in more white space, in addition to using a larger font size.
Last, just for fun, The Culture Trip created a list of 50 unique bookstores in every U.S. state. You can always approach one and see if they will sell your book!