Had a quick look since the 2009/10 domestic season. Lahiru Gamage & Vishwa Fernando were in the top 5 as per the following link.
http://stats.espncricinfo.com/sri-lanka-domestic-2015-16/engine/records/bowling/most_wickets_career.html?class=4;host=8;id=2014%2F15;type=season
http://stats.espncricinfo.com/sri-lanka-domestic-2015-16/engine/records/bowling/most_wickets_career.html?class=4;host=8;id=2014%2F15;type=season