Legal Question in Civil Litigation in California

Your remedy is to bring a motion to compel and to seek sanctions. In the meantime, if the documents are as important as you say, you may want to apply ex parte for a continuance of the MSC.

If you have a lawyer, she should already know these things. If you don't have a lawyer, you should get one now.

If you have an MSC date, you most likely have a trial date. That means you have a cutoff on discover and on discovery motions.

If a party has stated that they will allow production and inspection in response to a demand for inspection, and subsequently fails to allow production and inspection, then your remedy is a motion to compel compliance with their statement that production would be allowed. (Code of Civ. Proc., sect. 2031.320)

There is no need to attempt to resolve informally, and although there is no time limit, your discovery cutoff is fast approaching. You may have to get an order shortening time on the motion.