Here is the link to eBay's General Announcement Board, I believe this is the only place they list these promos.
http://www2.ebay.com/aw/marketing.shtml
You can also setup in your seller preferences to have eBay automatically send you these notices via email.
Please keep in mind though...that eBay's typical "advanced" notice is the evening before the promo starts. I received this notice around 7:30pm CT this evening.