You can certainly replace the breechplug, but that's not necessarily the simplest fix. Depending on whether you've done any filing/shaping on the first tang, and whether or not you've already inlet it into the wood, you might want to see if someone can tig weld the crack.
If you haven't begun to inlet it, I'd probably go with replacing it. Have you installed a breech plug before? It will require some time to fit it properly, so that it is seated properly both inside and out.
I doubt that Chambers would have a breechplug. They purchase their barrels with a breechplug already fitted.
Don't worry, your problem is definitely fixable.
Jeff
Good luck