I've heard rumors that one is coming, but that is just a rumor at this time. I have no facts.
The ammo carriers were also based on the E and F chassis as well as the D. Which is good, because that gives you more options for conversion than the old Tamiya D.
Italeri and DML both made "F" series Panzer IV's. That would be my suggestion of a starting point for a conversion.
Just my 2 cents.