Are the “letters” of Chinese language called characters or symbols? I’m sure they are not letters! I would prefer characters. Anyway, if you want to find a lot of Chinese characters-symbols-letters-alphabets however you call them, buy a dictionary!
I’m joking, you can go at http://www.wearyourchinesename.com/chinese-symbols/chinese-symbols.html where one Chinese character is added daily. You need to buy a dictionary only if you are serious about learning Chinese.
And, I should say, just a dictionary is not enough. You need a good dictionary, with examples and pinyin (not only the pinyin of the main word, but also of all the examples).
Anyway, lately I’ve found very, very useful the Pleco software for Android tablets. It’s really great and it’s free. I use it everyday (I live in China now). The feature I love most is to be able to copy/paste whatever Chinese text from any source (pdf files, the web, etc.) and the software let me scan each Chinese character and each Chinese word telling me meaning, pronunciation and example of usage. It’s really very, very useful. You can even pronounce a word and then, here it is!