How can I get more Resident Evil 4 Mercenaries Weapons?

I'm playing RE4 on ps2 and I was wondering how you get more weapons for when you play the Mercenaries mini game? I saw someone on youtube have unlimited ammo, and different weapons to use while playing the Mercenaries mini game, and also seemed to have a hefty stock of grenades. So how do I get unlimited ammo and different weapons? I have two star ratings usually and think if I have better weapons then I could get 4 star ratings. Please no cheat code links they barely explain anything.