I believe the thread was last week and if I were more technically adept, I'd post the link right here. But I know myself, and I'd probably post a link to something entirely inappropriate so...I'll just tell you to scroll down a bit. The subject line is, in fact, Ras el hanout!
house of spice in kensington market sells a good one. also has, besides an amazing spice selection, a great selection of pataks curry pastes in bottles and cans. many that i've never seen at any of the chain grocery stores
All middle eastern stores should have it - usually a selection of different mixtures. Many high end and Jewish stores carry it also. Bonnie Stern sells a great version, though it isn't cheap. (Bonnie also sells a dukka mix that is wonderful.)