Well, I don't know what the hell N-Track is, but if it supports VST plugins, there are many orchestral options. Some of the cheaper orchestral sample libraries are the Edirol Orchestral library and the Garritan Personal Orchestra.
Sampletank 2 kicks ass, and it has orchestral samples, though it's not a purely orchestral library.
There's always free Soundfonts on the net, so if you have a plugin that can play soundfonts, you might want to try that. I personally hate free soundfonts, as most of them suck balls, but hey, different strokes for different folks.