The data on the page are not available through the Dashboard API.
Options I can think of:
a - Look at the page source and create a script to extract the information from the web page or from the CSV links. But if the page design changes, it may break your script.
b - Use the scanning API to get the real-time data used to generate the presence data - this is how many analytics applications work. If there are a lot of wireless clients there's a lot of data!
https://developer.cisco.com/meraki/scanning-api/
c - Use a third-party service to do b) for you.
