To which department code should I send my TOEFL score?
As far as each department or university has it's own code for English tests such as IELTS or TOEFL; it is better to visit the admissions web pages of the universities or schools you are going to apply. If you do not find the code you are looking for, directly contact the admissions department to ask for their reference code for the tests. Besides, some codes of the institutes may be published on the website of each test (but the contacting the school is more sure in my opinion).

As a general rule in my academic life, the only sure source for such information is the website, help desk or contact person of the institute you are applying to. Asking these questions here or from your friends generally do not help you because they may not be sure about the piece of information they are giving and you may face difficulties for the wrong directions. So, always stick to the source of information you need to boost your progress up and avoid difficulties.