Should start to see it in a month or so, or call a local coop or Ufa. They will tell you when they start to get there summer shipments, will still be a blend for a bit until the volume in the tanks get diluted though
A few of the bulk dealers around us keep summer diesel all year round. They will bring it out as long as they can pump it. Usually down to -18 or so. A few calls to some bulk dealers might get you some now.