[Rules] How player characters might find items they need?

Simple rule. If player characters own a castle, spaceship or a dungeon they conquered last month there's a big change that there are items left behind from previous settlers. But it is too time consuming to make an imaginary inventory of every nail and board and toothbrush! Here's a quick solution:

 Can We Find It?

When players ask can they find item X in their place, there's one-in-X chance there is one of these items. The X chance varies by how rare and powerful the item is. A simple tool might be 1-in-3-chance (result 1 with 1D3) when an ancient relic to open dimensional portal to Limbo might be 1-in-1000-change (result 1 with 1D1000). Naturally the probablity of the desired item being found depends on a setting, and location where it is been searched. A tome of magic necromantic in nature is easier to find in old crypt than in a bakery.

There is a big change that the item is worse compared to an item your player have bought. But hey, these are free items you happen to find behind that cupboard or in the dusty corner of the hangar. 

Now that the item is or is not found, there are some other things you might consider. For example...

Condition

I am not going to write long rules for the condition, but you might roll a D4 to determine what's the abstract condition of the item. Result "1" is 25% of original condition, "2" is 50%, 3 is 75% and 4 is 100%, mint. Also if you rolled 4, roll again. If you roll another 4, the condition is 125% of the original! If you want to go crazy and roll another 4, just add 25% to the previous (exploding dice).

The condition might affect item in many different ways. Here are some examples how:

• Reduced damage every 25%. 75% condition is -1 to damage, 50% condition -2 and 25% decreases damage die one step (1D8 longsword now deals 1D6 damage). If item is in a better than original condition, the weapon deals one die step higher damage (1D8 longsword would do 1D10 damage).

•  Reduced protection. -1 per 25% below 100%. Better than mint condition adds 1 to AC.
•  Tools or other equipment you need to use to achieve something give penalties or bonuses to dice rolls. 1 bonus or penalty per 25% over or under 100%.