Sawsbuck is only available in the friend safari, not in any season affected areas (like the snowy parts). For this reason, if you count out the friend safari as much as the dream world for gen V (or perhaps more accurately, compare them to each other), technically, Sawsbuck isn't really in X and Y, so there is no need for seasons. Therefore, there is no way on X and Y to get all four Sawsbuck/Deerling forms without poketransfer.
Hope this makes sense and helps out a little