No idea about the Chariot hitch (though it looks like it should work if the diameters are compatible), but you could try emailing alix@simple-city.com (I think Carry Freedom are one of several brands owned by the same company) and asking if they'll ship you one directly. He recently got back to me about spares for the rubber axle covers on the Y-frame hubs, which aren't a standard accessory.
Failing that, I'm sure a friendly Brit could order you one and pop it in the post...
