The Lemmy instance slrpnk.net automatically provide a XMPP account as well with the same ID and password as your federated address.

I'm dont know if this is in line with the community but here are some server directories:

• https://list.jabber.at/
• https://providers.xmpp.net/
• https://jabberworld.info/servers/

This one is useful for checking feature compliance across different servers: https://compliance.conversations.im/