Once you reach 450 archaeology, the Tol'vir dig site have a chance to appear in Uldum.
That doesn't mean you automatically get Tol'vir dig sites when you hit 450.
They also only spawn in Uldum, so it may be the case that you have to keep clearing other dig sites in Kalimdor endlessly trying to get an Uldum site to spawn. The downside of the Tol'vir having most of the really nice rare items, I guess (Bug Mount, Crawling Hand pet, BoA lvl 85 epics, etc. etc.)
Does get a little demoralising when your first Tol'vir rare is that goddamn Scarab trinket with the 1hr40min cd (!!) though. 150 fragments takes a llllllong time.