AFAIK there is no such book, nor is it likely that anyone would write one.
Every C# book I have seen without exception teaches you to use C#, which is a completely different task to "here's some code, it's useful".
Besides, what is a "practicle program" or a "practical source code" for one programmer, would be irrelevant, or too simple, or too complex, or just generally rubbish to another.
There is however a wonderful tool for finding such things:
www.Google.com[
^]