looks simple enough, from the image there appears to be no tension flex like a standard pole banner bracket.
so go to your hardware store get a "T" aluminum pipe fitting that will fit over the vertical pole and then thread tap the the "T" fittings for a secure fit, with a tension screw.
then get either a reducer or the same diam pipe for your banner pockets.
A MUCH EASIER method is to get a traditional pole banner bracket with metal straps and then you don't have to know the OD of the pole being used
there are several MM here that sell supplies for mounting