The brief for the Center for Competitive Politics et al. is here. The ACLJ/Focus on the Family Brief is here.
More amicus briefs:
Senator McConnell
ACLU
Coalition of Public Charities (Bob Bauer)
Still more:
Chamber of Commerce
Alliance for Justice
AFL-CIO
Family Research Council, et al (Kathleen Sullivan, Stanford Litigation Clinic)
Citizens United
NRA
National Association of Realtors
Links to the earlier briefs here. (Disclosure: I filed an amicus brief in this case with Richard Briffault.)
Reply briefs are due April 18. Oral argument is April 25.