I found about 3 silver veins, about 5 tin veins, and about 10 Iron Veins in Arathi Highlands, but I guess it was my lucky day to what you guys have said. So Arathi Highlands is good for iron and tin, but not so sure on silver.

Try and look on a totally unknown place, called Unknown. Unknown where it is, just look there.

Hope this helps.

Alexbrute --> 70 Tauren Hunter --> Doomhammer Realm --> Horde