No subpoena duces tecum shall issue for the production of writings or documents used to reach the conclusion contained in a certificate of analysis prepared pursuant to § 19.2-187 except upon affidavit that the requested writings or documents are material. Upon a showing by the Commonwealth that the production of such writings and documents would place an undue burden on the Department of Forensic Science, the court may order that the subpoena duces tecum be satisfied by making the writings and documents available for inspection by the requesting party at the laboratory site where the analysis was performed or at the laboratory operated by the Department of Forensic Science which is closest to the court in which the case is pending.