Reddit reviews JW Winco Stainless Steel 303 Round Tapped Knob, Knurled, Threaded Hole, 3/8"-16 Thread Size x 5/8" Thread Depth, 1-1/2" Head Diameter (Pack of 1)
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Round tapped knob with knurled head styleMachined from solid barMade of stainless steel 3031-1/2" Head diameterRoHS compliant
That's almost certainly a custom machined piece. You can see in the breakout in the lower-left corner that it's 3 pieces: a pivot rod and two endcaps.
You might be able to use something like this along with a short piece of threaded rod: https://www.amazon.com/JW-Winco-Stainless-Threaded-Diameter/dp/B00A9N0DUU/ref=sr_1_6?s=industrial&ie=UTF8&qid=1483477353&sr=1-6