You can still use the same call (below) but filter the call on the serial number of the unit in question. However you need need to pass that serial in the call, which means you likely need to do another call to get that ahead of time.
You might be better off just running the over all Org call, say every hour, and then use your Application to just look up the data within the past results, without an API call. This public IP information doesn't change all that often.
https://developer.cisco.com/meraki/api/get-organization-uplinks-statuses/