The last spark plug spacers we bought were from NAPA
Normally they are only used as a temporary bandaid to keep the tractor running until you can tear it down and repair the problem.
used if you have a cylinder that is pumping oil for some reason that shortly kills a spark plug.
The guy at NAPA said to never use them on more than half of the cylinders at any one time.?????
As others have said, ask your auto parts dealer, you may be able to buy hotter plugs that will help keep the plugs clean.