You can vote for the BF3 8v8 Conquest ladder right here.

If you happen to be playing another game - this is where you can start a petition for a ladder in that game.
We will be happy to host ladders - but we ask the community to show us that they are interested in getting a specific ladder, and has some support in the community for it. That is what we are using the petitions for.

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Source:

BF3 8v8 Conquest Ladder