What is the problem with your current one, or is it just completely missing? It might be possible to repair the one you have, unless it is severely damaged, rusted out, etc. The only other option would probably be to find someone with a junker 216 or early 235 who would be willing to sell you the part. It's a pretty simple piece, which should be able to be fabricated with a little effort. The tough part would be getting the spring tension on the bypass valve right.
Jerry
