If you like German Sausage and want it from the Source then Mattern Deli in Orange is your answer. After years of buying Bochwurst (ingredients: Veal, Milk, Pork) & Bratwurst from Globe Deli in Costa Mesa I tracked down their source and Mattern is the manufacturer. Lots of other good German Deli items also besides the Dusseldorf Mustard.
Sandwiches $ 3.50- Closed Sun & Mon.
Mattern Deli & Sausage Co.
4327 E. Chapman Ave (not to be confused with that Fullerton Chapman Ave)