How do I know when my clutch needs to be replaced?

I have a 2004 ford focus ZX3 2.3 DHOC with the MTX-75 manual transmission. NOT SVT. I have racked up 115k miles. I have been doing some window shopping and have noticed that certain parts are very difficult to find. One of those parts is the clutch w/pressure plate including flywheel embly. Would the lack of general availabilty be an indication of Ford's belief that the clutch doesn't need to be replaced for a long time?