For a small charge UK marriage certificates can be obtained from the GRO (Government Record Office) - https://www.gro.gov.uk/gro/content/
However I don't know if they will deal with someone outside the UK.
To obtain a certificate you will need the volume and page number of the record which you could try finding using - https://www.freebmd.org.uk/
Hope this helps.
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Mark Lucas
UK