Hello, Kalonian -
The answer to your question as to where you can puchase a stopper for your Tefal soup maker depends upon the country where you reside.
Apparently, Tefal Repair Centers sell replacement parts for Tefal products.
First go to this web page:
http://www.tefal.com/country-selector
Select the country where you reside and click on the language link for that country.
Scroll down to the bottom of the Tefal home page for your location and choose Repairs. On the Repairs page, you should be able to find a Tefal Repair Center not far from where you reside (I hope), which you can contact to find out they can sell you a stopper for your soup maker.
Fixya.com receives questions from people all over the world, often making it a challenge to figure out the right information to provide.
Best wishes.
