As with all of these bikes of this antiquity, ebay seems to be the default destination for parts shoppers.
However, many of these parts are still available from Honda, since they were used across much of the model line.
A great source of information on three-wheelers is 3-wheeler world:
Make sure that you misspell words and use The Official Southern U.S. Lexicon by sprinkling words like "y'all" and "howdy" into your posts. You'll fit right in if you remember that Nascar is a religion and Lynyrd Skynyrd is eternal.