There is no general 'send email if resource is unavailable' action, youll have to either:
A. build this into each process, where you have a timeout or some other action that only allows the process to wait for so long before emailing you about a possible problem, or;
B. build separate process or processes that checks each resource by taking and quickly releasing the resource every few minutes repeatedly and emails you if it is unable to get a new resource after a set period.