Hubbard Spring has a minimum order of 100 on their disks.
I have bought some on ebay – $6 for half a cent worth of aluminum is pathetic
one of the major carb kits I bought last year included the welch plugs and lead balls,
but I forget who I bought it from.
they are on my watch list for the swap meet on Saturday in Lake Hamilton, FL
If you are working on a Johnnyrude, they will be in the OMC/BRP car kit. They usually include different sizes for different carbs so these can be saved for when you need them.