All the parish baptismal records were copied by the General Registry in 1910. This copy is indexed by church with surnames in alphabetic order and then chronologically. This copy may be consulted and a copy obtained from the General Registry; it is also available on microfilm at the Manx Museum. It is this which was used by the Mormons for the IGI

LDS films are given at http://www.ee.surrey.ac.uk/Contrib/manx/famhist/genealgy/ldsfilms.htm

the Manx Museum have microfilms of actual registers - I thought these were also available via LDS FHCs but I have never tried (my local FHC is open so seldom and has such a long queue I save up any requests till I get back to Manx Museum)