David beat me to the answer, but yeah, you'd need to reach out to the sales team to set up a PoC. UBA is not just an app, but is rather a series of on-prem vm's/server appliances that do the live analysis and session tracking.
Totally, definitely not just a Splunk App; UBA needs more data science tools in order to hit the high bar of that live analysis and session tracking. One adjustment: VM is not required, though that is by far the most common for a trial. It can handle Ubuntu or RHEL installs as well (http://docs.splunk.com/Documentation/UBA/2.3.0/Install/Requirements ), and there are also many AWS installs.
it appears the trial process has changed then since i set up our PoC environment. Last I had experienced it was 3-4 Ubuntu VM's, but then again we started with it when it was still Caspida. Nice to know they have a baremetal option for it now.