KZ305 rubber plugs impossible to find

Injected wrote:

If you want to reproduce that plug out of rubber on a lathe consider grinding it with rough paper or use a Dremel tool with a carbide burr at a fairly high speed (work piece one direction, tool in the opposite direction) Cutting rubber with conventional lathe tools only deforms it, the stuff is like chewing gum even at a high hardness.

I use to work for a rubber company doing prototype engine mounts, ground and carved a lot of different parts using all types of tools. Grinding it will give you a smooth uniform shape.

The Kawasaki version Mikuni BS34's use a pilot plug made from zinc, employing a small O-ring to seal.  I'd make them out of brass if it came to that, along with the O-ring.

You may be able to find some junk carbs for cheap from any of the below which use the same plugs ?
 

This may be worth a try.