Just saw this, when are you going out there? Sri Lanka as a whole is very relaxed, you can pretty much go fishing anywhere you like and bound to get inquisitive enquiries from the shore and water.
Its not heavily fished out, so you do not need to work hard to find some decent fishing. Buy some bait fish from the fisherman find a rocky outcrop, and you are off.
I was there about 4 years ago, and could not believe the sealife within wading distance. The area has a natural port - an assumption is that depth is close to shore with all its promises.
Look forward to any reports; I am back there in April. Then Northbound through Puttalam, Mannar, Jaffna and a couple of tanks to try and catch a Wallago Attu and a big a Snakehead as poss.