Searched and found nothing posted before. Sorry if it turns out to be a repost.
Tol'vir sites only appear in Uldum, and sometimes you can be waiting ages for one to pop up.
What I've been doing is digging just TWICE in the Tol'vir dig site, then waiting 15 mins (fly and dig another site then come back maybe), and hey presto, the site reset, rinse and repeat, dig twice, do another site, come back, dig twice.... etc.
This way the next place you dig is always going to be Tol'vir, if only for two fragments.
You can use this for other races too I guess, but the Tol'vir one is the most annoying for me.
Hope this helps some people.