正規表現を使用できます。
NSString *feed = @"Feed for 03/02/2012";
NSError *error;
NSRegularExpression *regex = [NSRegularExpression
regularExpressionWithPattern:@"([0-9]{1,2})/([0-9]{1,2})/([0-2][0-9]{3})"
options:NSRegularExpressionCaseInsensitive
error:&error];
[regex enumerateMatchesInString:feed options:0 range:NSMakeRange(0, [feed length]) usingBlock:^(NSTextCheckingResult *match, NSMatchingFlags flags, BOOL *stop){
NSString *month = [feed substringWithRange:[match rangeAtIndex:1]];
NSString *day = [feed substringWithRange:[match rangeAtIndex:2]];
NSString *year = [feed substringWithRange:[match rangeAtIndex:3]];
//...
}];