[DutchmenSport]

Well, this is a new one for me. I looked up "Anti Siphon Trap Vent Device or an ASTVD" and got hits on several different things. The first that came up looked like a conventional Air Admittance valve. The next thing that came up looked like something that came off the Space Shuttle. After that, that term produced nothing but confusing items with the same name. So, really, I have no idea what the original poster is asking about now.

But whatever it is, if it's something connected to the RV drain pipe plumbing, then to answer the original poster's question, .... "Yes", you can get the part from any Home Improvement store as the plumbing pipes (water and drain) are the same that's used in your home.