I've read all four of the series that you've put out to date and enjoyed all of them immensley.
I just hope you are not, but am afraid you are, the prophet of your day.
Volume V will be out in July. I was shooting for June, but with the death of my father in January and our taking my mother into our home for a few months, that work has understandably slowed down.
It will be well worth the wait though.