Most Lankan commemorative coins since 1995 have been issued with respect to 50th anniversaries celebrations Most of them were Non Circulating Legal tender (NCLT) coins, and since 1991 have been sold at a premium by the Central Bank. The few coins indicated below in bold font were minted in in larger quantity and released as general circulation at face value. See some comments.
1981 Universal Adult Franchise - 50th Anniversary - Rs 5 coin
1995 United Nations - 50th Anniversary - Rs 5 coin
1995 U.N. Food and Agriculture Organization - FAO 50th Anniversary - Rs 2 coin
1996 United Nations Children's Fund - UNICEF 50th Anniversary - Rs 1 coin
1998 Sri Lanka Independence - 50th Anniversary - Rs 5000 coin - Rs 1000 coin - Rs 10 coin and Rs 200 note
1999 Sri Lanka Army - 50th Anniversary - Rs 1 coin
2000 Central Bank of Sri Lanka - 50th Anniversary - Rs 1000 coin
2000 Sri Lanka Navy - 50th Anniversary - Rs 1 coin
2001 Sri Lanka Air Force - 50th Anniversary - Rs 1 coin
2001 Colombo Plan - 50th Anniversary - Rs 2 coin
2008 Employers Provident Fund (EPF) - 50th Anniversary - Rs 1000 coin - Rs 2 coin
LakdivcCoins Collection website.