The rubber bellows on my choke plungers have perished and cracked. Been looking all around for replacements, but cannot find any mention of them anywhere.
Just for kicks I put that part number into http://wemoto.com.au and apparently they can get them and quote $17.05 each. However, they may take a while to get them in.
You could try taking that part number up to a local Kwak dealer and see what they come up with.