It's unusual for a table to have that size opening without having some insert rings to snap in for using smaller bits with. Most of the Sears routers I've seen didn't have that large an opening in the baseplate to be able to use bits that big. With that said, even if your table did originally come with them I wouldn't want to bet that you could find some for it. Sears is bad about having parts for older tools.
One option would be to build your own table and add an insert plate that has the right opening as I really can't see an easy way to fix the one you have. I've built 2 router tables now for under $20 and there is tons of info on the site about making your own table. It isn't nearly as complicated as some people think it is. You can research it with our Community Search function or go to the home page by clicking on the Routerforums logo on this page and scrolling through the different forums until you find the one on router tables. Of course we will be here to answer questions and offer suggestions if you need. You just have to ask.
By the way, you can buy an insert plate from Grizzley for $13 that has different size insert rings. It's the President's special and the easiest way to order it is just call and ask for it.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
Last edited by Cherryville Chuck; 11-15-2015 at 11:49 AM.