Under the "Miscellaneous Specialties" section of the link below, it appears Watts still makes the FHB-1 w/ vacuum breaker. You can maybe order that and try to take whatever parts you need off of it. I used to work in a plumbing supply place and I don't remember seeing stand alone parts sold for sillcocks like this; only the whole unit. So I don't think you'll be able to just buy certain parts.
http://www.watts.com/pdf/F-LowPressure.pdf
http://www.watts.com/pdf/F-LowPressure.pdf