You can get your non-prescription reading glasses at the dollar store or drug store which has a large range of non-prescription reading glasses and you can go to select one that suit you best after trying them on. Or you can get them online. There are many online optical stores selling non-prescription reading glasses. So you can search them in the web browser, like google with key words. Then there will be a list of stores for you to choose.
You can get non prescription reading glasses from most optical stores, and it is quite easy to find them. But it is not suggested to get the non prescription ones if you are also nearsighted cuz non prescription reading glasses are made with the same power in both lenses. They are suitable for people whose eyes have the same power in both eyes. However, most people have different unique prescription. So the non prescription reading glasses may not fit your prescription and you may get a headache if wearing them too long. It is better to get prescription reading glasses based on your prescription.