Like I said, I'm not really sure that one exists. What you're looking for isn't exactly lightweight- you're looking for a pretty advanced piece of software that does a very specific thing. That might not be easy to find. I just did a google search of "loading large amounts of data to JTable" and got back some promising results though.
But this sounds like a job for a custom model, which you're probably already using. Storing the data only as necessary has been suggested, and I think you're putting yourself in a corner by just saying "that won't work" and looking for a third party library instead.