These are not my posts, but they're from a 4 part guide that I've used with great success to scoring threesomes with women. It's a very detailed and comprehensive guide, and one of the best guides on getting threesomes that you'll find on the web. All together the guide is pretty long read but very worth the read.

Part 1: Women and threesomes, threesomes in societies, and limiting beliefs : http://www.pua-zone.com/showthread.php?3693-The-Threesome-Guide-Part-1-Intro-and-quot-Beliefs-and-facts-about-threesomes-quot

Part 2: the type of men who have threesomes and what you need to get a girl to have a threesome with you : http://www.pua-zone.com/showthread.php?3787-The-Threesome-Guide-Part-2-quot-Who-are-the-men-women-have-threesomes-with-quot

Part 3 : Sexual re-framing, sexual prizing, and sexual qualification/disqualification : http://www.pua-zone.com/showthread.php?3892-The-Threesome-Guide-Part-3-quot-How-to-convey-that-you-are-a-potential-threesome-partner-quot-(Sex-talk)

Part 4 : Screening and handling resistance (making her want a threesome even though she's open to it but not yet comfortable with it) : http://www.pua-zone.com/showthread.php?5498-The-Threesome-Guide-Part-4-quot-Screening-and-handling-resistance-for-potential-threesome-partners-quot

Also, I made my own post about calibrating your game for threesomes: http://www.reddit.com/r/seduction/comments/1kmfqp/calibration_for_scoring_threesomes_with_women/