The ball vent was cobbled together from found items. I started with a 10" syrofoam sphere, flattened two sides on the belt sander, added a cylinder cut from 2" thick foam, then coated it with casting resin so I could smooth it out and paint it without the paint eating the foam.
For the tapered vent end, I cut a couple more circles out of 3/4" MDF, cut the middle out of one of them, and glued them together. Then I set the bench sander up on an angle so I could grind an appropriate taper to the sides. The louvers were 1/4" strips of 1/4" MDF that were cut to length and glued into place. The whole thing needs a bit more sanding and smoothing, then I need to paint it all shiny so I can mold it.