I'm not sure how far you are into geneology but you realistic best bet lies with electoral registers, censuses, parish records, and sites like ancestry.co.uk (I've on a family tree in that).
If I was doing the search I'd phone Richmond Registry Office and see if they have a marriage certificate - oh and while you're there ask if they've got a death certificate as you might as well get the possibility out of the way from the outset.
This individual appears to be very old, probably hasn't gone ex-directory, so if you know roughly where they live, you can call every 'Collins' in the phone book. Also 192.com gives you access to current electoral roll.