Good morning organsRgreat
Here is the link to Stephen Bicknell's article (which does not contain the compositions): https://www.stephenbicknell.org/3.6.19.php
I have found the compositions for St. Lauren's Alkmaar on orgbase.nl: http://www.orgbase.nl/scripts/ogb.exe?database=ob2&%250=1000654&LGE=EN&LIJST=lang
Mixture compositions for quite a few organs have been published in this database.
Franz64 made available a summary document with the mixture compositions of a few organs as well: http://forum.hauptwerk.com/viewtopic.php?f=2&t=6119&p=42877&hilit=Alkmaar+mixtur#p42877
The google docs link is still active.
Regards
Pharny