no on-line index exists
papers upto 1855 are indexed but the index didnt include BMD's
A card index to BMD's was being constructed by a volunteer worker at the Manx Museum - I'm not sure if it was completed to reach 1871 - however with the date a search of papers is fairly fast but needs someone to do it in person - the Manx museum have a list of professional researchers.

to be honest I suspect you will find little more than a notification but by this time some marriages were reported in more depth - however Maughold is back of beyond as far as Douglas was concerned (the Ramsey papers didnt start until 1880's - see http://www.ee.surrey.ac.uk/Contrib/manx/famhist/genealgy/press.htm