W1QJ - You are correct. I just checked Harbach and their parasitic suppressors are "out of stock". I had not looked at that site in a while.
I still think he could easily match the parasitic suppressors in the amp or just wind 3 turns of #10 wire about 1/2 inch in diameter shunted by a 47 ohm 2 watt non-inductive resistor (or 2 each 100 ohm 2 watt resistors) would work and should cost less than a dollar or so for all four.
The Ameritron suppressor looks impressive, but since the Clipperton uses 4 tubes, he would need a pair of the Ameritrons.
Any way this is not rocket science. Just get the amp going!