Actually you can buy prescription sunglasses in the opitical stores or on the Internet. For the local store, you can go to your original place where you buy prescription glasses and you can have an eye exam if your prescription has changed. If you have a valid prescription, you can get them online. The price is much cheaper online.
All right, i can see that you are looking for a pair of prescription sunglasses for the incoming summer. So, it is true that it would be pretty hard for us to get them. However, I have got some good tips for you, I would like to recommend Amazon and Alibaba to you, both of which could just provide you what you seek at a good price and their range of products is so wide. Just take a look at them.
When the summer is coming, the prescription sunglasses are very suitable for those people with short sighted problems. They could make you look fashionable and protect your eyes from the uv rays. You could find that in many online stores, like walmart, amazon and so on. The price there may be suitable. you could go to have a search.