In such cases, the word, 'if' can be omitted and the sentence can be transformed by interchanging the position of the subject (you) and the modal (should). The clause follows the pattern: subject+auxiliary (you should). We can omit 'if' by interchanging the position of the subject and the auxiliary  i.e use 'should you' instead of 'you should'. The sentence can be re-stated as: 'Should you need my help, I will always be available any time'. Hence, option C is the correct answer. 

Option A is incorrect due to 2 reasons: a) The word, 'If' is not dropped. b) a different auxiliary verb, 'were' is used instead of 'should'.

Option B: This sentence is in the past perfect tense. When the original sentence is transformed, the original tense (future tense in this case) has to be retained. Hence, this option is incorrect.

Option D:  This sentence is grammatically incorrect. This is because the verb 'were' is a linking verb which also acts as the main verb and another verb 'need' is not required in the same sentence. 'Were you in need of my help' would be the correct grammatical usage. Hence, this option is incorrect.