If you haven't found them already, these indexes prepared by the late Brian Lawson might be useful, now on the IOMFHS website under 'Research':

www.iomfhs.im/lawsons/wills/_will_index.html

www.iomfhs.im/lawsons/burials/_bur_index.html

There are links to some transcribed wills there, and there are more in Manx Notebook (see tab at the top of this page).

Brian also compiled birth and marriage indexes but I think a visit to a FHC is probably your best bet.