Yes, you can buy the harry potter glasses at walmart which is the popular type this year for its round lenses. You may spend about $30 for this type of eyeglasses. You could also go to the other online stores to have a comparison among the price. You may find the better suitable one.
It seems that you are really into Harry Potter products anyway. So, currently there are a lot of stores which sell harry potter products , costumes and glasses as well, and Walmart is one of them. However, sometimes not all Walmart stores have got their products on offer. But you can also have a look at other online shopping sites for them. Generally speaking, a pair of their glasses would be about 100 dollars.