Glory Swimwear has some pretty amazing mannequins. They honestly look like they belong in another sort of store. Besides that they have all of the swimming-related stuff you could want, at high prices.
Basic goggles are Rs. 850 - 7,000 (!), swim trunks are Rs. 1,350 up, body boards cost Rs. 1,500 to 5,000, and pool loungers cost Rs. 2,400 upwards. They have a wide range of stuff, from competitive swimming to lounging to diving. They also have a good and functional selection of women's suits.
Again, everything is expensive, but they do have everything and in good quality. If you're getting, say, board shorts they're actually not much cheaper in Unawatuna and the items here are much more durable. They also have a lot of items that you'll simply struggle to find elsewhere (good goggles, flippers, etc).
We apologize that there aren't more photos but they don't allow photos inside. We did get the suggestive mannequins from the street.
They have a fish with a weird growth on its head. Pretty cool.