Your best bet would probably be something like a
Topeak Versa Cage with a bag like the
Revelate Pole Cat or something similar. It looks like the fork only has a single mounting point, so you may need more mounting points to carry the load. The Versa Cage mounts are plastic worm gear clamps that can’t be tightened as much as metal worm gear can and, thus, don’t have as much of a possibility of damaging your fork. There are other cages and bags around but they all cost about the same.