Other double cursed affix combinations exist on these armors to give us the same probability of dropping. That brings us to a 1 in 76,000 games chance of stumbling across one. While they each individually have a 1 in 304,000, we need to divide by the 4 possible base items to see our chance of finding any one of those. There are other base armors that can drop that combination of affixes with the same probability: Plate Mail, Field Plate, and Gothic Plate. As an example, Vulnerable Full Plate Mail of Weakness has a 1 in 304,000(!) games chance of dropping and it is only findable in Hell difficulty. When thinking about the rarest item in the game, people often go to the double cursed items. One item that has always stood out is the Emerald Long War Bow of the Heavens at a whopping 1 in 16,200 games! It is arguably not necessary as you can use an Obsidian bow and attain maxed resistance, but it is very nice to find.
Given that Griswold can sell them to you, this is not terribly difficult to obtain. One exception would be a King's Bastard Sword of Haste with a 1 in 6500 games chance of dropping. The bulk of them have a roughly 1 in 1000-2000 games chance of dropping. Most of the end game items are easily findable given a few years of solid casual playtime.