I was searching for a way to get the url to the review overview for a specific location via the API too.
After checking the links, IDs ect. in the API Responses and lots of documentations an tuturials i found NO way to get the link over tha API.
BUT a workarround with a few manual steps can help to find the link (I know that is not a final answer to the question, but maybe it is still helpfull)
- go to google search, and search for you Location/ Company that contains the reviews
- on the right side you should see a pannel that shows the current stars for your location and a link "xxxx Google-Rezensionen"
- klick on this link and copy the url in the browser
(optional remove parameters like "&client" ect.
Check this youtube-video of the Step by Step Tuturial to see a tuturial how you can do this.