Install Fiddler, configure it so the store can connect localhost (win8 config). Now trace the Windows store web traffic and you will see the URLs that the Windows store is using like:
https://services.apps.microsoft.com/4R/6.2.9200-1/615/nl-NL.nl.en-GB.en/m/NL/Apps/4bd603d9-21da-4282-a689-b2a4f384717e/Reviews/all/s/date/1/pn/2
