There's a great Korean restaurant on University Blvd called Sam Won Garden Restaurant: 4345 University Blvd S Ste 1, Jacksonville, FL 32216.
Not sure if they serve blood sausage but they are pretty authentic. There's also a Korean market on Beach blvd just north of University, they might sell it there.
Korean might be a problem, but there lots of ethnic meat markets in Jacksonville & vicinity. Look for the German meat markets selling blutwurst and the Polish markets selling kiszka. Both pretty close but I think the Polish version makes heavier use of blood. Beware of the Jewish version "kishke" which looks the same but has no blood. (still good though)