You don't have to worry if one or more compelling evidence is not available for sharing; In-fact, it should not bother you at all, and all you have to do is to mark it in our system as "Evidence Not Available" - It will inform us that you have reviewed the requirements, but you are unable to provide them, which will allow us to submit the available evidence for the dispute.
Bare in mind that we are requesting the evidence only after we have evaluated the existing evidence that is available to us and after the system detected that the requested evidence could significantly increase the winning chances of the dispute, so either way - we will make sure that only a vital, and a rock-solid-response will be submitted.
Additionally, if the evidence is marked as not available, and becomes available for you before the due date, click on "Evidence Available" and update the evidence in the system.