Help! I need a new barrel!

I have a CVA Frontier model rifle I built fro a kit when I was 17. I desperately needs a new barrel and I can't find one anywhere! Green Mountain says their barrels won't fit my breech but nobody seems to be able to tell me why. Can anyone out there tell me what I have to do to my rifle to make a new barrel fit it? A new tang, perhaps? A different lock plate? WHAT?