Tim, I agree that it's silly to leave the jovibarbas out of the Sempervivum database, but here's the solution. When you search for Sempervivum, you arrive at this page:
http://garden.org/plants/searc...
Instead of clicking the link for the Sempervivum Database, click the link that says "View all plants in the genus Sempervivum." That will bring you to a list of all the Sempervivums, including the jovibarvas.
http://garden.org/plants/brows...
Click on the "L" at the top and scroll down to Lemon Sky.
http://garden.org/plants/brows...
You can also avoid all of this by searching in the main database instead of the Sempervivum Database. If you search for Sempervivum Lemon Sky, it comes right up in the results.
http://garden.org/plants/searc...