When the Sigma 19 mm f/2.8 EX DN lens profile will be avaliable in Lightroom 4?
I believe we have profiles for all currently-available (i.e., in production) Sigma lenses. Is the 19 f/2.8 in production? If not, that would explain why we don't have a profile for it. If that's the case, then it's unlikely we'll be providing one soon, but as John mentioned, it is possible to build one yourself using the free Lens Profile Creator.