(Not a teacher)
I find coming up with examples of 'disadvantage to...' difficult, so perhaps it isn't as common as 'for' and 'of'.
'Disadvantage of' means that the object of concern creates or has the disadvantage:
'A disadvantage of the radio is interference.' - the interference is a disadvantage that the radio has.
'Disadvantage for' means that the object of concern receieves a disadvantage, or rather, is affected by a disadvantage:
'A disadvantage for the radio was the invention of the television.' - the invention of the television affected the radio in a negative way.