I am actually plotting the next arc of Last Shot in my spare time, as I do intend to finish it one day. Though, there are no official plans as to when a new issue will come out. Though, rest assured that when it does, we will probably rerelease a new TPB of the first arc with new stories inside that will cover scenes that occur in between a of the past issues in order to remind people of what Last Shot is all about.
Having said that, please don't hold your breath. As I said before, there are no solid plans at this point in time.