Map of Tasmania Surf Spots.

Few tips
(1) Don't book anything get the free camping book before you come there are lots of magic spots where camping is free e.g. Preservation Bay on the Northwest Coast, Chain of lagoons East coast.
(2) Unless you like the cold, come now or before April but be warned it can turn cold very fast, so pack a good wetsuit.
(3) make sure you give yourself plenty of time lots of people think they can see the entire Island in a week, there is lots to see
(4) make sure you get to cradle mountain, no surf, very very cold but is paradise
(5) dont tell anybody how nice it is we like the lack of crowds

Around the northwest coast the hot spots, (probably not the right word for surfing here) are at a place called the Midpoint Rocks ( Sulfur Creek ) and the Devonport River Mouth. The point break the east side of the midpoint rocks would be just what you are after when a northeast wind comes in. Beach breaks around here are at Preservation Bay, Coles Beach Devonport, Boat Harbour Beach. Boat Harbour beach is a real nice spot well worth a look but for some reason the water is always about 5 degrees colder then the rest of the coast.
There is free camping at Preservation Bay and Sulfur Creek.

If you go about 3 hours west of here there are point breaks at Trial Harbour and Marrawah. Normally the west coast beaches have much more size and some pretty wild weather conditions.

To the East about 4 hours is the East Coast scamander river mouth is a nice spot and you can camp just south of there. Otherwise on the east coast take your pick.
Down south everybody talks about Clifton Beach but mainly Cloudy Bay Bruny Island.