I haven't been to Madid. But I think you can search the eyeglasses stores in Madid and then you can find many results. But why not ask a local people where you can buy a pair of ray ban sunglasses. It is not as difficult as you think. Hope you can find a ray ban sunglasses store very soon.
It's so easy. Ask your mum or your dad or all of your relatives. I often buy sunglasses online because the sunglasses sold online are much cheaper than that sold in any real stores. It can help save money. I think the quality of the sunglasses is OK. But the size was a little... I had them changed later. So if you want to buy a pair of sunglasses online, you must know the size of the sunglasses.
Many physical shops will give discounts when it's time to celebrate their anniversaries. And on many holidays, there are all kinds of discounts in any kind of shops. I think eyeglasses stores will hold some activities or give discounts too. So you can have a look on any special days. Hope this helped! Good luck!