Nice. Those go for a pretty penny on ebay. At least compared to what they use to cost new.
When I redid my grande after prying off the top instead of trying to replace it, I replaced it with a plumber's plug like this, only in the right size. That one was just the first example link I found, though mine is the same exact style. Those ones are a lot better than the ones with the big wing nut on top because it lets the cap sit down fully. Almost as easy as a screw top.