This information will be included in detail in my General Guide and my Bestiary and Caves Guide for Rune Factory 2 on Monday, but for those players who are frustrated by their inability to obtain a couple of items, the solution to this is to use a Magic Spell.
There is very little in any Harvest Moon game that does not have some purpose and Rune Factory 2 is no exception. You need to have the Inquisitive Waltz Spellbook and the aid of a Tame Monster to find the elusive Poison Powder and a couple of other items...
Rune Factory 2, like Island of Happiness, is such an immense game even where its basic plot is concerned, that one may be inclined to forget that ALL Harvest Moon games include secrets that are not obvious to the player and which must be discovered.
When one begins to use the Forge and Workbench in the 2nd Generation, one finally can use the War Trophies one has collected from Monsters in the Caves. As the list of items grows, one may assume that all rare items that cannot be grown as crops are 'dropped' by Monsters. This is NOT the case, however. There are a few rare items that must be 'found' by a Tame Monster.
The use of the 'Inquisitive Waltz' in this game really is quite wonderful. Once again, I am reminded of playiing the flute for my dog in 'Save the Homeland'. That was one of the best options in that game.
Here is a little visual tutorial on how to find and use the Inquisitive Waltz to uncover the rare Poison Powder.