No, there isn't, if they've never been built "large." But you can choose a large size (say 256x256), and then they will be full thumbnails at any size up *to* 256x256 (i.e. if you go to 128x128 and then back to 256x256 you'll get the full thumbnails).
Not sure of this makes sense in the explanation, but if large thumbnails were never built, you'll need to build them. This makes the catalog smaller by default, I guess.