When you setup the local FIND server you setup the group. I would setup a local broker then you don’t need ssl/tls. You setup the MQTT the same way you did for the external server, but point it to the local one.
This thread will help with FIND…
HA setup
sensor:
- platform: rest
#minute: 30
resource: https://ml.internalpositioning.com/location?group=<name of group you setup on server>
value_template: '{{value_json.users.<username>[0].location}}'
method: GET
name: My Internal location
scan_interval: 60
Mine is still pointing to the external server as for the moment I can’t setup a local sever, tho’ I may have a play with the windows binary’s 
Edit: Seems the windows stuff is fingerprinting only, so still need a linux server 