Looking for information

I take it you've already seen the parish record of the marriage on Irish Genealogy website ? Bride's surname is given as Kensington.

http://churchrecords.irishgenealogy.ie/churchrecords/details/6202ec0557…

Although this doesn't include father's names it goes give places of residence for the bride and groom, which could be useful clues. A civil cert should include father's name and occupations, and also occupation for Andrew. These are the most likely BMD Index references :
Name: Andrew Gallivan
Quarter/Year: Jul-Sep 1900
Registration district: Kenmare
Volume: 5 / Page 153

You can use these references to order a research cert by fax or post costing €4 from the GRO. Download the order form from this link : http://www.welfare.ie/en/Pages/Apply-for-Certificates.aspx

The possible brides with the same reference should also appear on the index, but in this case there seems to be a mis-match on the index and just three names are showing - Mary appears on the index as Kennington same district and quarter but with slightly different references - i.e. a volume 1 / Page 153, and the only person with these. Still worth a try... but maybe mention both sets of references when ordering.