Hank,
Ask you local nut and bolt / fixing man if they stock trapezoidal, ours do, never bought small only 16mm and I can't remember how much it was, they also have like a barrel but to suit.

I accept you will have to get some machining done but this post is also a heads up for other people,

If I have a length left I'll get a pic later, still after that bloody cat..........