This is the second firearm found through Madush.
The Police said that a T-56 firearm was discovered in Dalupotha Ela in Negombo.
Madush had pointed out the location where the weapon was hidden, the Police said.
He was deported from Dubai and arrested at the Bandaranaike International Airport (BIA) in May and detained by the Criminal Investigations Department.
Madush was among several Sri Lankans arrested at a hotel in Dubai in February at a party.
Most of them arrested were drug dealers and other criminals.