This is how I found it;
1) Selected the search box in the top right
2) Selected the option to search apps
3) Pasted in, UI Examples for 4.1+
4) Clicked on the link for UI Examples for 4.1+
5) Arrived at http://splunk-base.splunk.com/apps/22333/splunk-ui-examples-app-for-41
You have to install the app into Splunk and then open it using the Apps menu...if that's not working for you, please provide more detail about the steps you are taking.
Have you tried clicking on the Download button to the right? You then have to install the app through Splunk by going to Manager -> Apps then click the button that says install app from file. Navigate to the file you've downloaded and like magic its there...
However, if you're struggling with even this step you may want to stop and read the tutorials before trying to do any UI dev