Fosters & Smith carriers a small variety...
http://www.drsfostersmith.com/produc...?N=2001+113215
My local pet stores carry one or other as well... I've heard the citronella ones don't work quiet as well as the shockers, and they don't do well with picking up high pitched barking/yelping.
My parents used a remote shock collar for training their beagle.. They didn't use it for barking, they were field training her. It sure did make her stop in her tracks. But eventually she learned if the collar wasn't on, she wouldn't be shocked, and she could run as far away as she wanted....
I'm not really a huge fan of any type of citronella/sonic/electric collar. Have you tried anything else to stop problem barking?