you might have to buy a parts manual of of ebay.
here is the link.
it is 28.00 on ebay
http://shop.ebay.com/i.html?_from=R..._nkw=john+deere+21s&_sacat=See-All-Categories

 

Here's a link to a JD 21S. A 21SX dud not show up on their parts catalog.

http://jdpc.deere.com/jdpc/servlet/com.deere.u90490.partscatalog.view.servlets.HomePageServlet_Alt

 

Found it on there thanks dutch 1.

http://jdpc.deere.com/jdpc/servlet/com.deere.u90490.partscatalog.view.servlets.HomePageServlet_Alt

I found that site there myself but the model no. did not come up.
But looked on there again and did equipment search.

 

Thanks for the information!