August is a great time to get fresh lobster as the second lobster fishing season (around August 10th) is just starting up on the south shore! Getting fresh lobster is fairly simple you can go right up to any of the harbours on the south shore around 11 am- 1 pm and you can buy freshly caught lobster right from the fisherman! Or in Wellington, there is the Acadian Fisherman's Co-op. There you can buy live lobster or processed if you choose along with a variety of other fresh seafood! As for the fresh shrimp, you may have to travel a bit further to North Rustico. There you will find Doiron Fisheries and they have fresh Atlantic shrimp (one of my favourite summer treats)!
Hope this helps you out!