I don't know about what Larbel used...
From what I know, replica brass "obi valves" are no longer made. Replicas made by Romans Empire or JediVic can sometimes be found in the Junkyard.
There seems to be consensus about the brass knob on the original prop being a "valve adapter" for bicycles. As far as I know, the exact match to the original has not been found, but I have seen maybe half a dozen ones that each could be considered close enough. All the ones I have seen have been too tall. The head may need to be ground or cut down a bit.
That is what I used for my own replica. I put a 4 mm hemispherical amethyst inside it, because it looks right and is a real gem stone. I don't remember what I paid for it, but it was at least not more than $5. I got it from a store that sold gems and catered for would-be goldsmiths.