Hello...
As the divorce was over 100 years ago you can view their divorce file at Dunedin Archives. The divorce file often, but not always, contains a copy of the marriage certificate.
http://www.archway.archives.govt.nz/ViewFullItem.do?code=10626935If you're unable to get to Dunedin you can either pay Dunedin Archives to photocopy the file and send it to you (usually a charge of at least $25) or start a new thread entitled "Dunedin Archives look-up". Include the above link and, on his/her next visit to Dunedin Archives, a kind Rootschatter will take photos of the file and email them to you.
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I have completed a massive chunk of my family tree, but it's come to a halt with my great grandparents
As mentioned, the newspaper article in reply #4 says there were no children.
No children = no grandchildren = no great-grandchildren.
What makes you think they are your great-grandparents.
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A Frederick SWAIN married an Agnes RUSSELL on 24 Sep 1907, a few days after your Frederick's decree absolute. Possibly a second marriage for your Frederick?
You might want to start an
ITM look-up thread for both the 1888 and the 1907 marriages. Might have some info. Might not.
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Where did you come across the name Beustbolt. Not a common name at all.
Regards
Beg