I grew up in Chicago, and my mother shopped at a variety of kosher butchers. That said, in Chicago, the understood rule is that all kosher hotdogs need to come from Romanian, an old style kosher butcher. Today Romanian is the only kosher butcher left in Chicago (there are lots of places to buy kosher meat, but Romanian is the only real butcher). Watch this fun video about Romanian. I’m not sure if my favorite part is when he admits they have bad service, or looking at the random boxes piled around the store.