I've become a bit of a history buff, and curious: What was the situation in Sri Lanka at that time, what was Major Bayly's military orginzation and mission in Sri Lanka in mid-1800's? Or was he a missionary? Which denomination?
FindAGrave.com is international and has a terrific cemetery search engine, and name search engine. Free. Many overseas cems have been surveyed and memorials posted on that site. When you have accurate info on his burial, you can create a memorial for Major Bayly, then request a volunteer in that country to photograph his grave, post the photo and send you photos too.
If you can learn some history, pershaps there will be clues to follow up. Try the international sections of FamilySearch.org, the huge genealogical records/books, etc. of the LDS Church. Ask for their assistance, all free.
Have you tried Ancestry, or Google, and the links there? Also Google Books for publications not under copyright.
There may be web sites for his old organization, or books on the subject at Amazon. Have you searched for his records at the VA site? Try writing to the National Archives in Washingdon DC. The researches there do an amzing job.
Also search the Surname message board for Bayly and for Hammond. Post your query on the Surname message board for both Bayly and for Hammond with as much info as possible. http://boards.ancestry.com/surname
Sounds like a very exciting project for your family. If you ever locate his grave, do post your findings on this message board. Good luck!