Determining End-Of-Life for electronic components
There are few professional services which integrate notifications from manufacturers and can manage your BOM:


IHS: PCMS, BOM Manager, PCNAlert, etc.
SiliconExpert 


Probably others I'm not aware of.

Most of big companies in aerospace and defense business subscribe to one of these services but they have dedicated component management departments.

Also only few components really need attention for EOL notifications, for instance memories (DDR). EOL notifications are submitted almost 1 year in advance so you can check the PCN on a monthly or weekly basis of few manufacturers for your critical components.