It depends on your definition of metalcore, but I suppose I will answer this assuming As I Lay Dying / Underoath are somewhere in that range.  First off a good place to check is Facedown records (www.facedownrecords.com) primarily hardcore / metal also Come And Live (www.comeandlive.com) though not primarily hardcore have some decent metalcore acts.  Both labels give out nothing but Christ Centered music and would be a good place to start to find some good new stuff.  Some of my personal favs would be A Plea for Purging, Onward to Olympus and Fallstar.  All have very solid lyrics and music that pumps me up.

As to your second question, that is much harder to answer.  As I Lay Dying has some stuff on their site you could check out (http://www.asilaydying.com/faqs.html).  Not that Wikipedia is the source for the best knowledge, but Underoath's WikiPedia (http://en.wikipedia.org/wiki/Underoath) has some stuff to say about this.  Scroll down to the "Christianity" section check out the blurb and search the references it sites.  That should help you get well on your way.