There's a guy selling repro ones on ebay. They're only 9.99, and match the originals. The funny thing is that they aren't smooth and glossy because they haven't been used for 20+ years. They have a mat finish that should turn smooth after use.
I bought one for my spare Tempest panel, and it fit right on. The only other difference is that there is just one set screw that holds it to the spinner shaft where the original has two.
For 9.99 you pretty much can't go wrong.