or use a derived column(note that this will not work if numbers use leading 0's):
Result = !ISNULL([Col]) && ((DT_STR,20,1252) [Col] == ((DT_STR,20,1252) (DT_I4) [Col] )) ? (DT_I4) [Col] : 0
All solutions taken from this link:
I prefer the script component method myself. I'm don't know VB, but it's simple enough code to understand and apply.