Electrum has a list of default servers which you can find here: https://github.com/spesmilo/electrum/blob/afa1a4d22a31d23d088c6670e1588eed32f7114d/lib/network.py#L57. However there is no list of all Electrum servers just like there is no list of all Bitcoin nodes. This is because Electrum servers are distributed like Bitcoin nodes and anyone can run one. Electrum has a peer discovery protocol which you can read about here: https://github.com/kyuupichan/electrumx/blob/master/docs/PEER_DISCOVERY.rst. The Electrum servers will connect to each other and ask each other for a list of other Electrum servers each peer knows about. So each Electrum server builds up its own database of other Electrum servers. Then when a client connects, it asks the servers it is connected to for a list of other Electrum servers and the client also builds up its own peer database. The message for getting a list of other Electrum servers is servers.peers.subscribe and you can read about that here: https://github.com/kyuupichan/electrumx/blob/master/docs/PROTOCOL.rst#serverpeerssubscribe

So if you want to find available Electrum servers, you can begin with the default Electrum servers. Then ask each server for a list of other Electrum servers, connect to those, and so on and so forth. You do this to build up a local database of Electrum servers.