I think I may know the Shermila Gamage you are looking for. She was my best friend in high school at lived in Dehiwala - born in 1973.
Although we are seperated now (I live in the United States), I can try to get you in touch with her through another high school friend of ours.
Please get in touch with me via email at firstname.lastname@example.org
and I will forward you the information of our friend Thilani.