You should probably replace them with the same B&W tweeter.  Substituting another tweeter without modifying the crossover will likely not work or sound right.
 I am not familiar with a DM602 SE (nor does B&W list an SE model for replacement parts), so did you mean S2 or S3?  B&W replacement parts are available at 
http://bwgroup-support.com/partspriceavail.html DM602 series tweeters are available as complete tweeters or just the diaphragms.   
DM602:      ~$72 complete tweeter / ~$58 tweeter diaphragm
DM602 S2:  ~$83 complete tweeter / ~$58 tweeter diaphragm
DM602 S3:  ~$109 complete tweeter / ~$83 tweeter diaphragm 
Steve