I have heard the term 'petcock' before, perhaps in a marine context - contraction of 'petrol cocks' presumably.
Those Birkin ones are very different to the ones in the op. The ones in the op seem a pretty simple CAD/CAM project - remove one, dismantle, scan, import to CAD and fiddle the design to accommodate modern off-the-shelf seals, send it to the multi axis milling etc machine, and after a trip to the industrial supplies shop for the seals you are good to go. Two thousand quid for the suckers, fifty quid for you (mates rates, as long as I get a drive ). That would be my OOM cost (guess), there may be more on the other side of the tank that might add complexity/cost though.
If you can't find an original supplier, that would be my next step anyway.
On the other hand, those Birkin ones look like you could get them on Fleabay … at least the brass part, they seem like a different philosophy separating the bend in the line from the tap. Sorry, 'petcock' .