I emailed the address given on this page:
"I would like to know when a Zerolemon extended battery + case will be available for the Galaxy S4.
Do you have any information regarding this that you are allowed to release?"
I got a response early this morning, saying:
Thanks for your interest.*
This will be available in next 2 weeks.
Please check here periodically for availability: http://www.amazon.com/s/ref=bl_sr_wireless?_encoding=UTF8&field-brandtextbin=ZeroLemon&node=2335752011"