Bill,

Replacement Carbine barrels are available. 

You can order a Criterion barrel from the CMP.  It will come "In The White" which means that it is un-blued, and does not have the front sight post installed.  It will be properly machined for the extractor cut and for the front sight post.

You might also try Numrich.  They definitely have 30" rifle barrels, and I have heard they do have carbine barrels, but I can't say for sure.  If they do, it will come blued and machined, and with the front sight post installed.  I have heard of some people being unhappy with barrels from Numrich.  I have ordered other parts from there, and had no problems... so I guess it's a crap shoot.

IMHO, I would go with a Criterion barrel.  You would have to finish it and have a proper sight post installed, but they are very good barrels.  I recently replaced my Garand barrel with one from Criterion and it's great!

Best of luck... and let us know how it turns out!
Paul