As you do not have any public services to accomplish this, I would suggest to use the below services (at your own risk) and build a wrapper around it. You can schedule the service at regular intervals, if CSQ count is >=1 and send out email alerts as required.
wm.server.jms:getCSQMessageCount
wm.server.messaging:getCSQMessageCount
However, you can explore Optimize for Infrastructure to see if SAG has provided any OOTB KPI to monitor and alert on CSQ count for both native and JMS messaging.
#Integration-Server-and-ESB#webMethods#Universal-Messaging-Broker