The main development site and GIT repository for these drivers is https://linuxtv.org.
The DVB mailing list linux-dvb is hosted at vger. Please see http://vger.kernel.org/vger-lists.html#linux-media for details.
The media subsystem Wiki is hosted at https://linuxtv.org/wiki/. Please check it before asking newbie questions on the list.
API documentation is documented at the Kernel. You'll also find useful documentation at: https://linuxtv.org/docs.php.
You may also find useful material at https://linuxtv.org/downloads/.
In order to get firmware from proprietary drivers, there's a script at the kernel tree, at scripts/get_dvb_firmware.