Nothing compares to SG Balkan Flake in bulk that I have found. This is one of my favorite blends and is in my regular rotation. I just by the 250g boxes and cellar them. Buy three boxes from Smokingpipes and some pipe cleaners, and get free shipping.
True flakes with latakia are pretty darned rare. MacB HH Latakia Flake is a nice altertnative to SG, but it's not available in bulk, and you sure aren't saving any money. dcrguns is correct - just get SG Balkan in the 250 gm packs.
Lancer Slices come in bulk. Personally I like it better than Balkan Flake. Smokingpipes.com is always out but 4noggins seems to have it whenever I order.