All newts are salamanders, and there are many species in the USA that are commonly bred. Spanish ribbed, Danube Crested, Alpine, Bluetail firebelly, Marbled, Kaiser, Lake Urmia newts are all found regularly in the fall when the newts are morphed and ready. Some of the more rarer species of newts can be found if you are patient and have money.
Now if you are referring to terrestrial salamanders, the reason why you don't see them captive bred is very easy to explain. Cost. There are many states in the USA that allow the collection of native salamanders. In certain times of the year it is very easy to take them from their breeding areas and then the various large internet reptile webstores sell them, cheaply. Breeders spend a LOT of money and time and work to raise salamanders from an egg all the way to a morphed individual ready for sale. I.e. my electric bill for just June was $377 and my blackworm bill was about $400.
Look later this year for some captive bred Western Tiger Salamanders from the site founder John Clare. He's been working hard at raising up some for the hobby. Otherwise get yourself a newt.
