I am looking for one of these: The part that screws into the manifold looks to be 1/8" pipe thread. The other end is 5/8 thread for a flare fitting. it is used to connect the brake booster vacuum pipe assembly to the intake manifold on a 1967 GS400; it might be used on other years as well. It looks like this when attached to the vacuum pipe: I only need the brass fitting, I have the pipe. Thanks for looking.
Go to your local auto parts store. Most have a selection of brass fittings. ALSO your local hardware/home improvement store have brass fittings.
I have them in stock if you still need one. https://www.diecastmusclecars.com/BuickEngineBayParts.htm .
I stopped by my local NAPA a couple days ago. They were out of stock but ordered a few for me. I will see what they come up with.