Randy Day wrote:

I'm looking for an electrical coupling to provide 120VAC
to equipment on a rotating platform. The platform can
only turn one way, so it can't have wires up the hub.

Is there a commercial product out there, and if so, what
is it called? None of the electrical places I talked to
knew of anything like this...

They are called slip rings. There are a number of designs, but typically
it's a couple rings of brass with carbon brushes that press against them
to conduct the electricity. They are used on everything from tank
turrets to ferris wheels. Very similar to the commutator on a DC motor,
but the rings are not segmented and provide a continuous connection.

Pete C.