int iWeaponPieceChance = RandomGenerator.nextInt(45);
if (iWeaponPieceChance == 44) {
addItem(588);
This is how the game decides if you get one or not.
The game randomly generates a number between 0 and 44. If that number is 44 you get the item. If it isn't, then you don't get anything.
By all means let me know what you might need! There are some items that I always skipped (200 wand, 75 boots, etc) as they were expensive to buy and a pain to drop. Others are easy as they are shop items (150 shield, 150 legs, etc) and I tried to do those ones all the time. Others were kind of in the middle as they were easier to drop or I had a lot of them (100 club, 150 bow, etc).
If it seems like a pain to get the item just skip it.