Download community version:
https://next.nutanix.com/t5/Community-Suggestions/Community-edition-Download/m-p/24304#M176 ( How to )
https://www.nutanix.com/products/community-edition/
If the Nutanix AHV is based on the supported KVM version and has nested virtualization vSRX should work just on any KVM platform.
But there is no official support for vSRX managed through Nutanix Prism/Acropolis.