Answer: No, this would not be considered standard English. The correct way to say this would be "I could have come if you (had) needed me."
Note that you can contract "could have" into "could've", so another correct way would be "I could've come if you needed me."
Explanation:
- Most native English speakers use the contraction "could’ve" instead of "could have" in everyday speech. This pronunciation omits (removes) the stressed H sound that differentiates "have" from "of" in spoken English, so some people mistakenly write it as "could of" when going off of pronunciation alone.
- While not technically an issue, the use of the word "had" in "if you had needed" is an unnecessary use of the word, as "if you needed" would convey the same meaning. If you would want to make your writing more concise (giving information in clear, short sentences), the omission of "had" is recommended.
- The use of a question mark here would be improper grammar, as this sentence is a statement, not a question. One way to make this statement a question is "Could I have come if you (had) needed me?" Note that the use of the contraction "could've" is grammatically incorrect here, as its use would turn the sentence into "Could've I come if you (had) needed me?"
Hope this helped!