@Russell Thanks for reaching out. Unfortunately, there are no property that can help you with the number of peek locked but the complete call was not made on a particular message.
As this is the message level property (DeliveryCount) so the delivery count will only be available at the message level when you try to read the message and not at the queue level.
When the message is failed to consume by your application then the DeliveryCount of individual message increase by one.
If you need the count at the queue level then you need to have your custom logic for the calculation, but I will not suggest to peek all the message just to get the DeliveryCount of the individual messages and adding them to get the current count for the queue as this would be expensive operation peeking all the messages.
Let me know if you have any queries or concerns.