Most people think that getting an unclaimed Twitter username is hard/impossible/a long process. However, if you’ve got legitimate grounds for asking for a specific Twitter username, they’ll usually get back to you within 48 hours!So what qualifies as a legitimate request? Well, Twitter has a policy that if you own the .com domain or if the account has been inactive for 6months+, you can apply to claim it as your own.So what if you meet either of these requirement? Well then follow the step-by-step instructions below to claim your username:Checkout: https://support.twitter.com/forms/impersonationMake the selection for ‘I ambeing impersonated.’Follow all the steps and fill out the form.Be sure to make the description of why you thinkyou should get the Twitter handle as concise as possible. This is where you should tell them you own the .com and any other entities related directly to the username. If you have any other registered trademarks or wordmarks for the name you should include this as well.Typically, within 24-48 hours, you’ll get a response from Twitter support with directions on how to proceed.Now you’re ready to start building a social audience on Twitter!

http://guides.co/blog/how-to-claim-an-inactive-twitter-username/

more info
http://qz.com/197227/complete-guide-to-twitter-handles/