You can get a free domain at dot.tk However, you must have an existing website and I think they redirect some of your traffic. You might also want to read this, http://www.itp.net/news/10255332171337.htm
I'm not sure why the ban, but I do know that a ton of .tk domains are being used for spam and other illegal means. Many people in China don't have credit cards and are securing the free .tk domains. I can only speculate since a large amount of spam, hitbot traffic along with hacking and software cracking originate from Chinese domains.