As of April 1st, SQL Server has been made available to download. If you have a MSDN subscription you will be able to download the bits. If you don’t have an MSDN subscription you can download the evaluation bits on the TechNet evaluation center.
Remember! In order for SharePoint 2013 to work with SQL Server 2014, you will have to wait till the Cumulative Update April 2014 is released!
TechNet link to SQL 2014 evaluation: http://technet.microsoft.com/en-us/evalcenter/dn205290.aspx
SQL 2014 Virtual Labs: http://technet.microsoft.com/en-us/virtuallabs?id=F2Ft/ah2g8Q