Estwing makes a geology rock bag that ought to be about what you would want. It isn't cheap, but it should be durable. I have no direct experience with it. I would consider mounting the bag on an external frame purchased second hand, something like a Kelty, Jansport, or Camp Trails. You could mount just about anything on the frame in addition to the rock bag. I have carried fossil mammoth tucks on one and other weighty fossils, and they would be perfect for a Pulaski or similar tool/ They would also be easy to customize.

I would also consider just sewing one up, using good, durable Cordura. That would be cheap and satisfactory.