Well, you have to play at night (around 11 PM) in the Mines at the Digital World. Then wait patiently for Bemmmon to show up and attack him to get his data. He is a very rare view, but can show up very earlier. Then try to get his data. I used a Digimon with maxed DEF and minimun ATK, SP and HP to farm him. You need two of them to make a fusion to get Snatchmon, then, level up him to 80 and them have 30 Gunslinger Fragment (crashed satellites).
So there was the chance to get Vemmon's line here? I mean not sure why the name changes as i remember playing DW3's european/english versions, but from what i remembered the Rookie was called Vemmon right? Snatchmon's okay, but still not sure if by Ragnamon you mean Galacticmon or is it another intermediate stage before it? Sorry for my lack of information, i last played the game on version 2.1.1 and had no idea those Digimon got here until now, still nice to see, didn't hear from that Digimon line outside from Digimon World 3/2003 which was kinda sad, those made a nice unexpected final boss honestly and i was among the guys who didn't hate that game when it came out, as i played it in my childhood for years and also cleared it. xD