Now a days we, normally, operate more than one account at different websites. Its happen that the name we desired is not available at one site if available at other site. There is a website which can solve your problem in this regard. USERNAMECHECK offer you to check the name at 68 sites. Most of the sites are user generated or popular messaging tools.
Now it will solve your problem of finding one username for all site. Just, you have to write desire user name in search box at the top and press button CHECK. You will know that the name you wanted is available at which sites.