They'll be free whenever the next pack gets released - probably mid-April.
I've got to download the map pack, I tried ranked BTB yesterday and all I'm getting is Valhalla. I was hoping that by the time I had money to buy the map pack, they would be free. Shame. Any idea when they'll be free? If it's not within this month, I'll go buy some points on Tuesday (I suppose I'll be able to buy Rez at the same time).
And yeah, BTB Ranked only includes (as far as I know) Valhalla, Sandtrap, and Last Resort.