Random spawns. No other way to acquire them atm afaik. You can use the Inferno campaign 4th scenario as my colleague has mentioned to get all three. I;m sure some new way to get them will be introduced in teh patch.
Just at the start of the 4th scenario in the Inferno campaign if you move to the left you will find a stack of fire elementals guarding an artifact. This artifact can be any random item in the game INCLUDING dynasty weapons. It will spawn something different every time you load the game or restart the map. Being so close to the starting point of the scenario (literally you can get there in the 1st turn) it;s a great way to get missing weapons albeit time consuming. It is afaik the only way to get the 3 weapons above w/o using exploits.
Thunder Staff: Orc campaign / map 2 / "Blood" quest - "Might is Right" (also bugged)
Sword of Whistlebone: Orc campaign / map 2 / "Tear" quest - "Time for New Ways"
Malathua’s Cleaver: Orc campaign / map 2 / Main quest - "Wild Card" L.E. (also bugged)
Check the thread at the top near this one for some fixes to missing Weapons. Pretty much all the ones that come from quests as rewards will or can bug out and not appear, you have to force them with a little fiddling with Heroes, Custom Games and Experience.
But I've gotten...18 Dynasty Weapons so far from playing through the Prologue and all five Campaigns (just got up to Stronghold map 4).
The 19th would be the Tears reward from Stronghold map 2, which I'll go back and get in a replay. But all of them have gone into my Dynasty, some needed the workaround, all were quest rewarded.
Only ones I have left are the 2 Gold/Platinum rewarded ones, and those 3 uniques that don't have an official location yet apart from that little trick. Maybe Edge of Chaos can be obtained that way too, seeing as I'm retail and got shafted on the Pre-Order bonus.
In any case, if I can remember any details about locations/quests, I'll be sure to post...but at the moment I don't recall a lot apart from what's been listed already.
I could compile the workarounds in a new thread when I get some time, but with a bit more neatness for those just looking to get their fix.
And at the same time I could also do a list of all the Weapons in the same thread, with locations and such. And get these two unstickied when it's done and the new one stickied in place of them.
At the moment I just want to finish off the last map in Stronghold and do the Epilogue before I settle down and go over some details like the exact depth of each weapon location/quest, and so on.
But if it was preferred, I could get it done pretty quickly (probably only a day or so to go through the workarounds and document the best retype...and about ten minutes for the weapons), after I've finished my playthrough.
A thread free of all the comments and whatnot, so people don't have to go through a whole lot of babble to get to what they need.
Wildcard is the term used for unique weapons that currently have no official location in the Campaigns, the Thunder Staff has one...Stronghold Campaign, Map 2...Blood Path quest.
Those Wildcards are Dragon Flame Tongue, Perfect Silksword and Staff of Sar-Aggreth. The rest have official known locations from quest awards, quest drops from hero kills, or quest locations for pickup.
The 3 mentioned above currently have no known existance and considered "only" random lucky drops from an artifact loot, be it intentional or not...and therefore a Wildcard.