Q: I have lost or deleted my iChat application for Mountain Lion--how do I retrieve or get another one downloaded?

I have no idea how I deleted the iChat application--have looked everywhere and in my applications folder when I click the iChat icon with (no access sign/symbol through it) it says "Can't use this versio of applicaton iChat.app with this version of OS X"  You have iChat app 5.0.3".  I don't have that version anywhere.  I updated from Snow Leopard to Mountain Lion about 6 weeks ago--I may need the new version of iChat but where do I get it?