Where do you get Queen's Decree?

I have looked through the forums and online, but all I find is people selling it or just talking about it. I am just wanting to know where and/or how to get it.

Pretty much anywhere. Most unique items don't have any set location to drop — they can drop randomly from any monster in any zone, as long as it is high enough level. That means that the chance of finding any particular unique is very low though, so your best bet is to trade.

Divination cards can help get specific unique items, but there isn't one for Queen's Decree. The closest is The Gentleman, which gives you a random unique sword (and therefore won't help much).