Im not convinced that any of Microsoft discounts/special offers are aimed at a particular time of year? You just have to keep your eyes peeled. Normally a Microsoft discount/special offer will be on a particular subject eg. virtualization.
http://www.microsoft.com/learning/en/us/special-offers.aspx
Prometric were recently running exam pack special offers, before the exam price increased, but this has now ran out.
Not really a direct answer to your question, but if you are after a way of discounting your exams, then ebay often have people selling exam vouchers (often with a few weeks left to run on the voucher) at a discounted rate. I have never purchased one of these
so cannot vouch for the eligibility of these.
http://www.ebay.co.uk/sch/i.html?_nkw=microsoft+exam+voucher
Hope that helps you
