"Need for", if used exactly as it is, is just a different and improper way of saying "need of". example: (improper) "I have need for your services." (proper) "I have need of your services." "Need of/for" is almost always used after the verb "to have" and is followed by a noun/noun phrase.

I also wanted to know the difference between them, so I looked up 'need' in the dictionary. Longman Dictionary said: The most common noun patterns are a need for something and a need to do something : her need for friendship | a need to preserve the environment !! Say there is a need , not 'it is a need'. Say a need for , not 'a need of' : There is a desperate need for cash. You can also use the expression be in need of something : We are in need of funds (NOT We have a need of funds). The dictionary seemed to tell me that 'need of' only comes after 'in'.