This gadget appears to only be available in the Cloud version.
Hi Nicole,
I am not on the Jira Service Desk Team but I will try to help.
Here is the list of the available gadgets for JSD Service:
https://confluence.atlassian.com/servicedeskserver/gadgets-for-jira-applications-939937318.html
You could create an issue filter using JQL count() and then use the 'Filter Results' gadget to display your results.
Alternatively, you could have a non-count() JQL filter and use the Issue Statistics gadget.
I hope that helps!