I was in the same spot when I put a crate engine in my 88 Blazer and needed to come up with a vacuum port for my brake booster.
Go to
www.firstgen.com It's a Camaro site, but it's got a downloadable catalog in PDF form. Once you download it go to the CATALOG'S page 219. They got several varieties there.
Another option is
http://performancesst.com/customer/home.php My impression was that they aren't OEM type stuff but will make a fitting with whatever you want.
Why the hell those things are so hard to find I have no idea. I had mechanics, autosupply stores, and online searches turn up nothing. One autoparts store even told me they don't make them anymore, so he made it a practice to take them from salvaged cars whenever he could and kept them in his toolbox. Geeeez....