Try this,
For Long Term Support (LTS) branch -( Recommended) Stable release
http://update.joomla.org/core/list.xml
Short term support (STS) branch
http://update.joomla.org/core/sts/list_sts.xml
Testing versions.
http://update.joomla.org/core/test/list_test.xml
All these XML files have link to their details zip files.
Hope it helps..