Replacement parts are not cheap. Here's one:
PDASmart - Touch Screen / Digitizer for Axim X5
Another option is to purchase a broken X5 on Ebay, etc. for parts only.
Before you buy anything, however, take a look at this thread for troubleshooting ideas:
Tapping screen not working consistently.
And don't forget to try a hard reset and make sure the batteries are fully charged.