You can download Model papers for 2017 GCE O/L (Ordinary Level) Examination here. These Model papers were prepared by well experienced teachers in Sri Lanka:
New Model Papers for 2018 O/L exam
O/L 2017 Maths Model Paper by Lahiru Kadurugamuwa
O/L Mathematics Model Papers were prepared by Lahiru Kadurugamuwa, University Undergraduate, who conducts O/L Mathematics Classes at Piliyandala.
O/L Model Papers for Science, Sinhala and Other Subjects
2017 Model Papers from e-thaksalawa
Sinhala Language and Literature සිංහල භාෂාව හා සාහිත්යය