Does anyone know of a php script that can crawl a site and check if the links on each page (internal or external) are working?
We should have been more clear. This is not an ordering site where you can freely get what you want handed to you on a silver platter. There are ways to do it. If you want to put forth the effort of creating a script, then we'll help. If you just want someone to do the google searching for you, you're in the wrong place.
I've told you how this can be achieved. Either you're willing to put in the time it takes to look up the regular expression functions PHP has to offer (there are only two sets) or you're not. If not, I suggest you go to hotscripts.com or find a free lance PHP developer to have them do this for you. I could probably put this together in about 2 hours worth of work. So it may take a new-comer to php a day or so to get something like this working.
The basics of it are:
1.) Get the HTML of the page(s) you're crawling
2.) Run a regular expression on the page looking for all valid links
3.) Use some function to validate that the links are in fact valid.
