This is a giant country - 300 million people or so, from what I'm told. But you'd think I could find a little round piece of plastic to whack into my plastic casks. Apparently not, at least not the right kind. I managed to find a source over on the East Coast that provides the Eurobung shives (at right in picture), but the diameter at the sealing surface is 1 mm too much. They also have a peculiarly designed hole for the spile, which not only takes a more profound whack with the mallet to penetrate, but then engulfs too much of the spile making it difficult to gently remove so as to ascertain the conditioning of the beer
But the shive on the left - ahh, there is a shive to die for. At 52.3 mm at the sealing surface, they mate nicely with the plastic CypherCo firkins. I kept this last used unit as a memorial to what a great shive should strive to become.
So, for all you alert and discerning readers, please contribute to the proper sealing and venting of real ale casks in Oregon by dropping a few hundred workable shives into a cardboard box and mailing it to the Brewers Union Local 180 in beautiful Oakridge, Oregon.