By "Reef Ready," am I correct in assuming you mean an all-in-one plug and play style aquarium? The kind where you don't have to fuss with buying separate pieces/parts?
If so, there are few models that would be big enough to house tangs. I would look at the Red Sea MAX systems. The 250 model (65g) would be acceptable for a Kole tang or POSSIBLY a Yellow tang (only one tang in this tank please!!!) but no other species of tang would be a good idea.
However, the Red Sea model 650 (175 gallons) would be able to house a greater variety of tang species. Anything but the largest tangs would be OK in this. It's a big tank....with a BIG price tag....but it does have that advantage of being stylish and all in one. Look at some of the big online aquarium companies via Google to see who will ship into the Great White North. Good luck!