This V1 API call for vpnStatuses will pull the VPN subnets.
vpnstatuses = dashboard.appliance.getOrganizationApplianceVpnStatuses(organization_id, total_pages='all')
Simple loop to get all in use subnets by location. I may have a sample python script that does just that if you need it.
{'deviceSerial': 'Q2PN-****-****',
'deviceStatus': 'online',
'exportedSubnets': [{'name': 'Office', 'subnet': '10.21.180.0/24'},
{'name': 'DMZ', 'subnet': '10.21.181.0/24'},
{'name': 'Wireless', 'subnet': '10.21.182.0/24'}],
'merakiVpnPeers': [{'networkId': 'N_*****************',
'networkName': 'Datacenter********1',
'reachability': 'reachable'},
{'networkId': 'N_*************************',
'networkName': 'Datacenter***********2',
'reachability': 'reachable'},
{'networkId': 'N_******************************',
'networkName': 'Datacenter*************3',
'reachability': 'reachable'}],
'networkId': 'L_***************************',
'networkName': 'Remote Location **********1',
'thirdPartyVpnPeers': [],
'uplinks': [{'interface': 'wan1', 'publicIp': '198.###.###.###'},
{'interface': 'wan2', 'publicIp': '47.###.###.###'}],
'vpnMode': 'spoke'}