Correct me if I'm wrong, but can't you just download the packages from https://packages.debian.org/wheezy/apt and install them manually using dpkg?
That being said, you can try verifying the sha256 and you might catch "them" that way if they didn't think of that.
I think it's true that without certificate pinning (which you sound like you know about) the various government agencies may easily have people inside your certificate stores that can issue bogus certs. That we've never read of one of these attacks succeeding is further evidence that the conspiracy is working ;)
Original trust is a problem with no possible solution inside a computer.