Start a chat with an entire Team of which you are not a member

We have a need whereby we want to have chat-style communication between teams, in which all members of multiple teams participate for real-time communications (for example, a need to reach out and contact anyone who might be available this instant). However, we don't want to proliferate a whole bunch more teams just for the purpose of doing this. We already have teams established that would be the "targets", so we just need a way to initiate a chat by specifying the team name or email address. For example, we have several 2nd level support groups each with their own Team, and we want a 1st level Service Desk agent to be able to initiate a chat with one of the 2nd level groups with consultation questions in real-time. 

We've considered Yammer, but it does not have the same immediacy of a chat to get people's attention in real-time. The desktop notifier app does not appear to have granularity to choose only to notify for a specific channel.

Is there a way to do this? Or a way I'm not thinking of?