I don't think that many IOM records are online. Brian Lawson & Frances Coakley have quite a lot of info available on their sites.
Depending on where you live, the easiest thing is to get microfilms from the local Mormon Family History Center. The Mormons have filmed most all of the parish records and it is inexpensive to rent their films, make copies--at least in US where I am or in Canada.
You probably know that the IGI is online at familysearch.com and it will give you extractions of parish records of christenings and marriages.
Let us know what you're searching for and perhaps we can all be of help to you.
Regards,
Donna