For south Slavic last names:
č- "ch" as in cheddar or the choose so same as "cz" in polish
ć - "tj" ...this one is hard, and only some dialects pronounce it differently enough so using "č" is good enough
ž - same as "J" in french names "Jeanne d'Arc" or Jean-Luc Picard
dž - same as "J" in the word "John" or "Jordan" or G in "George"
đ - just use dž
š - "sh" as in short