Abortion is illegal in Sri Lanka exempted only from the fact that if Pregnancy is a threat to mother's life.
So., you have either of the Four choices.
1. Keep the baby
2. Go for an unsafe abortion., which has a 50%-50% of going either good or bad. The best way to find the "best" doctor is to go an meet a PIMP. Chaps in and around Pettah usually knows the best doctors and places. OR if you want to check it out easily.. try the ISG forums on Sri Lanka.... there are some absolute hardcore mongers who knows their trade
3. If you got money... jet to a place where it is legal. Pakistan, South Korea, Thailand are countries where they offer legal abortions. You might have to check on their scrutiny laws regarding offering abortions for non residents / visitor visa etc.. but I am sure you can work something out on it.
4. This is Sri Lanka....

... where money "wisely spent" can do you wonders. All you need is a willing doctor and a willing hospital attendant to make you wife looks like she has a terminal illness...
OR
What you need is an already terminally ill woman of your wife's age... and an excellent forger or a willing middle man to make an ID with your wife's picture in it for hers.
The solution 4 is actually not so far fetched as you might think. I have come across on many who does that.