OK, question is, is there a chart somewhere that provides a quick rundown of which slot provides which type of stat? What I am really interested in is Doublecast, not which items, but it seems like some gear/weapon item types have doublecast while others do not and I want to know if it is slot related such as primary weapon vs finger slot.
DC is predominantly found on cloaks and belts. The bulk of the stat will come from these two items. Occasionally - cloth chest, charms and necklaces will have DC on it too. I think there was a hat in SoH Raid that had some DC on it too. Don't forget about green adorns with DC, as well as mount gear (saddle) that may have DC. You can search by that statistic on eq2u if so inclined - just be sure and search by stat, and not effect description.
Even easier, go look at EQ2U's Item Search. In the "Statistic" box, select Doublecast. Put in any modifiers you want (level range, class, etc.) and Search.