There is no such alert email as far as i know.
You need to keep track of the websites listed in this page for each province and also keep following this great forum.
As far as I understood, Saskatchewan open its application in-take once a month. usually in the first week... Just keep opening the webpages...That is what i did...
Its open now for SINP EE if you are ready to apply.
http://www.canadavisa.com/canada-immigration-discussion-board/sinp-ee-is-back-with-another-500-applications-dec-2015-intakeapply-quickly-t385529.15.html