How do you get blkbomb 3 in Megaman battle network 3?

Use a walkthrough. They're found on gamefaqs.com and myriad other gaming websites. Or, use a YouTube walkthrough. There are plenty of those. But don't use this media for that kind of question. It's infuriating and pointless, since the question is so vague that anyone who wants to answer it would be forced to outline the story itself and write a walkthrough in response to your question.