I have noticed that it's quite easy to get all the Winter dragons (re-released today through June 9th) by inter-breeding them.
For example, if you already have a Reindeer Dragon, you can breed it with any other cold or plant dragon and get a Gift Dragon, or you can breed a Gift with a Reindeer and get a Mistletoe Dragon.
Breeding some seasonal dragons (Seasonal or Spring + Winter) may also get you a few of the Winter dragons, though it has proved harder to get a Winter Seasonal using that combo.
So, by breeding any of the four together or with any other dragons, there a high chance you'll get all of them before they leave again on June 9th (and probably won't come back till next Winter/BEB).
Hope that helps anyone who's been trying to get any of those four dragons~