How to go about getting a Spouse Visa in Sri Lanka.

It shouldn't be difficult to get visa.  Contact a SL consulate in your country or ask her to ask around in Sri Lanka on how to get your visa.

Hi,
Firstly you have to be married before you can apply.
Once married , your Sri Lankan wife has write  a consent letter, with this letter and with her in person you go to the immigration for interview.
If they are convinced that you are married for real and not for some other reason to get a resident visa, you will get 1 year resident visa in your passport.
After a few years with a 1 year RV, you ask for two years they will give, your wife has to issue each time a consent letter , even if you get 2 years.
( they may consider also a 2 years visa immediately ( i don't know since i applied for it years after as earlier i was on a investors visa through the BOI, so i was not bothered about it until i retired.   
You can not work in Sri Lanka , hence you can conduct a business ( consultant or some sort )

Hope this answers your question
Good luck