I’m probably going to put the source up shortly but how I decided to find communities is by scraping my instances “federated with” list from https://toast.ooo/api/v3/site

Then going through the /.well-known/nodeinfo -> /nodeinfo/v2.0.json (or whatever url the well-known gives) to check the software to make sure it’s a Lemmy instance

Then using the Lemmy rest API to paginate through the open communities for that instance