Welcome to the forum. Sky One are currently repeating season 4 in the middle of the night, but because these are repeats they don't get added to catch-up so you have to watch them live (as alive as you can be in the middle of the night!)
However if you'd rather wait for the boxset to appear the NOW TV team have mentioned it should be available in December on NOW TV.
What about previously aired episodes of the latest season, how come they aren't on NowTV?
I can understand the episode currently airing not being available but this season started 2 months ago and we still can't watch episode 1 on NowTV. I might as well cancel my subscription as i only watch GOT (up to date on this), and The Blacklist
Welcome to the forum. S5 has started in the US but it isn't starting in the UK until sometime early next year. Once it does start airing on Sky One you will be able to watch it live and on-demand on NOW TV as well.