Believe it or not....Costco.
Also Jeff's Gourmet Sausage and it's Kosher too.
Vienna makes both a mild and spicy beef Polish Sausage but they are hard to find in the LA area. You can buy them directly from Vienna at their web site.
I love the spicy polish sausage at Fab in Woodland Hills. I've never tried their regular, but if the spicy is an indication, it is probably excellent.