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Don't know if you have found this, but:
athas.org/events

Kalak's death is 190th Kings Age,  year of Priest's Defiance.

How long before Kalak's fall do you want? 164th King's Age is when Dregoth is killed. 165th King's Age is when the Dragon starts his Levy to strengthen the seal.

 

In most of my campaigns, I've been pretty vague about the exact timeline (being flexible for narrative purposes), but in Dark Sun I've found it necessary to be pretty exacting about it. There's a ton of important stuff that happens as history moves on, and I'm also making it important for my players to be aware of the "coincidences" when certain things line up (they haven't put them all together yet).

Obsidian Portal has been very useful for this--I keep calendar information on three wiki pages there.

Here's the basic Athasian date information:
www.obsidianportal.com/campaign/the-lost...

Here is a list of years:
www.obsidianportal.com/campaign/the-lost...

Note that my campaign begins one year AFTER most Dark Sun campaigns. I set the date of Kalak's assassination on the first of the year--the gladiatorial games where he was killed was part of a huge celebration as the completion of the ziggurat coincided with the first of the year--and my game started the day after the one-year anniversary of his death. So your game will probably be in Priest's Defiance or earlier.

As the game goes on, I add important dates to here:
www.obsidianportal.com/campaign/the-lost...

There is also a huge secret DM's section of that last wiki that nobody can see but me; I add events from it to the public calendar as the PCs find out about them.

Note that I did not write/create the information in the calendars above; it was taken from the Dark Sun books, plus from some web sources, and then changed a bit to fit my own campaign.