Not to disappoint, but silver is a rare spawn of tin, and tin veins aren't especially common themselves. The southern barrens (and into thousand needles) has a fair bit of tin if you are Horde, but that doesn't guarantee much success finding silver ore.
If you need silver to craft something, you're best off buying it as it isn't very expensive on any AH I've ever seen. If you're looking to skill up mining, you're better off hunting other types of nodes.
Edited, Aug 10th 2006 at 8:23pm EDT by Hoobastunk