Yes in some cases although an arraignment is where you enter your plea. it's not an evidentiary hearing. May I make a suggestion? It sounds like you don't understand the legal procedures and the law very well. I would really suggest that you hire a lawyer or have a public defender appointed.
It is not necessary to obtain a subpoena. Once known to the prosecutor, evidence and information must be disclosed under ABA Rule 3.8(d) as soon as reasonably practical. Also, the landmark decision of Brady v Maryland (1963) places an affirmative constitutional duty on a prosecutor to disclose exculpatory evidence to a defendant. However, it is unlikely that you will receive this information before the arraignment.
The above answer is for general information only. It is not "legal advise" but analysis, and different lawyers may analyze this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.