i was just looking through the grainger catalog.
they have many fixed bore pulleys of cast iron, zamak, and glass reinforced nylon
a fixed bore pulley will be sufficient for your needs
you'll probably want an A belt(4L) pulley
If I were going to do it I'd cast a blank, but then I'm set up to do not only casting, but to alloy metals and to heat treat those alloys in an inert gas oven. The tools are pretty cheap, a wooden box and some casting sand for cheaper material like steel and aluminum. ... A wax pump and investment for the centrifugal casting machine mounted next to my bench grinder for things like gold, silver, platinum etc. (you'd think I'd have made a shield for it already given that if a mistake is made there's molten metal flying around the room at waist level...) I wish I could afford a large vacuum casting machine, those things are sweet.