If you are researching Calau, you might want to contact Sylvia Kolley who has done a lot of research about the Jewish history in the area and is also the author of the web site I mentioned earlier:
Sylvia Kolley
Luckauer Str. 57
15926 Heideblick
Telefon: +49 (0)35454 181990

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Andreas Schwab, Montreal, Canada

This web site (in German) is dedicated to the history of the Jews of the Niederlausitz region, which contains Calau:
http://www.luckauer-juden.de
You will find several pages about the history of the Jews in the region.
A list of names is found here:
A-L: http://www.luckauer-juden.de/nvz1.html
M-Z: http://www.luckauer-juden.de/nvz2.html

The birth records up to September 1874 will be at the Brandesburgisches Landeshauptarchiv. The archives are closed due to COVID-19 and will not be opened before January. They can only be used in person, and the documents will have to be ordered in advance.
https://blha.brandenburg.de
https://blha.brandenburg.de/index.php/benutzung/familienkundliche-anfragen/

Those from October 1874 and later will be at the  Archives of the Oberspreewald-Lausitz district. 

Bürgerbüro
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Andreas Schwab, Montreal, Canada