An old-timer I used to know made his own from plastic drain pipe. He used
a
lathe for cutting a spiral grove in the pipe for the wire, and machined
most
of the other parts himself.
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Before using drain pipe check it for RF integrity in the microwave oven. The
grey stuff seems to have metal containing pigment.
The white stuff might be better .....suggest you always check.

Another possibility might be a polystyrene cylinder in the shape of a liquid
volume measuring gauge as used by photographers in the dark room .
I have such a gauge made by JOBO - Germany , volume 500 milli-litre
,diameter 65 mm ( approx 2.6 inch), length 200 mm (8 inch).

Frank GM0CSZ / KN6WH