I am trying to send an XML message from my existing Python application to the existing SonicMQ JMS ESB broker deployed in our organization.
I cannot seem to find any Python library to send JMS messages to SonicMQ. The only one I could find is Spring-Python, which seems to implement only the connection to WebSphereMQ.
Is there any Python library to send JMS messages to SonicMQ?
Talking about Python and JMS is a bit of a red herring. JMS is a Java API standard into various messaging products. It's not a messaging product itself.
The way I'd think of this is...

Is there a Python interface to the specific SonicMQ product. I have no background w/ SonicMQ but a quick google search mainly brings up your question so my bet is no.
Is use of Jython an option, using its capability of calling Java APIs? If so, I'd expect Jython could talk to any JMS implementation using that. So yes you should be able to use JMS API to use SonicMQ just like a Java app.
Can I send JMS messages from Python to SonicMQ?