Stavanger, it is not that difficult for you to get Sri Lankan Citizenship as you were born there, and one of your parents were Sri Lankan once upon a time.
HOWEVER, please note the the country whose citizenship you presently hold, MAY revoke your citizenship if you try to get a citizenship of another country!
Please look into that, and re-think your wish to get Sri Lankan citizenship, is it because you wish to buy land here?
If so, there are many other ways of doing that, without incurring the 100% tax applicable to foreigners buying property here, please contact me for further details.
Best of luck, Sam.