Judging from past collections, starting next Monday for the different retail stores (Nordstrom and Macy's are usually first up, but worth looking at the others as well).
Also keep in mind that a LOT of other things sometimes get restocked on MAC's site--this week a lot of the Extra Dimension mineralized products were restocked, including blushes and EDSF's that read "sold out" a week or two ago (no way to know that ahead of time tho).
I've also had good luck calling MAC stores once the collection hits to do phone orders. Sometimes I'll try a pro store, other times I pick a small town where there isn't likely to be much foot traffic. The problem is paying the $7-10 shipping fee, esp. if you only want one or two items. Still beats eBay prices tho.