Truesilver is a rare ore. It usually spawns on the same nodes as mithril ore.
You are best to farm in Winterspring:
And in Thousand Needles:
There are some standalone truesilver veins in Silithus, which may make it slightly more profitable to farm there. But normally they share spawns with Throium veins.
You can also mine the following gems and stone from Truesilver: