Well, it worked out well, but a little clarification is in order.
The thread on the microphone stand is 5/8 -27, and the only source for a nut that size that I could find was Grainger, and one must have a business or trade connection to buy from Grainger. As an alternative, I suppose one could tap the inside of the arm to hold the fixture.
To hold the track light fixture, I bought a canopy socket and mounted it on a standard electrical box with a rotary switch installed in the side of the box. Then the box was mounted on the end of the microphone stand. The microphone stand came from Muscian's Friend.
Also, be aware that there are several varieties of track lighting sockets, and the fixture and socket must be the same type.
It was a non-trivial project, but like the OP, I couldn't find a suitable desk fixture for this bulb either.
I'd like to hear how others have approached this problem.