Find a cheap mop, broom, or push-brush where the head can be unscrewed from the handle. Saw off the mop part so you're just left with a threaded cylinder of wood or plastic that goes onto the end of the broomstick. Sand or rasp the edges clean as needed. Embed that cylinder into the ferrule (the part where the blade is connected to the handle) of your blade. Lock it in place with some epoxy adhesive (don't get any epoxy on the threads).
The name of the pipe you are talking about is PVC pipe. At that diameter, it is a little wobbly. A wood, metal, or composite broom handle will be much sturdier.
The technical name of the "cellular plastic" you're talking about is "closed-cell polyethylene foam". It's great stuff.
If by "pipe thingies" you mean the blue hoses, see if you can find 1/4'' or larger soft copper tubing. It should be sold at the hardware store in a coil. It is soft enough that you can bend it by hand, but once you bend it, it becomes work-hardened, so it won't bend back. This is good because it will give stiffness to the otherwise flimsy foam blade. Cut each piece to length either using a specialty pipe-cutter, or a hacksaw. If the tubing you get is too thin to match the prop, you can wrap the tubes in sheets of craft foam (technical term PVA-foam) to get the desired diameter. Use spray-adhesive to get the foam to stick to the copper tubing (or to get the foam to stick to more foam if you need to use multiple layers).