Dragon Age Origin Offer files missing

You're right that the old links are all dead. I can only assume that yes, they have taken down the server. 

I don't have any official live links to share, but I was able to find some of them using google search on sites where others have uploaded the .dazip files. I don't know how EA feels about the legality of getting the files that way, but if they aren't going to provide them to customers who have legitimately purchased the content, I'm not sure what other option we have.

I found this for Stone Prisoner and I can confirm it works in game. I installed it using daupdater.exe which accepted it just fine:  http://filemare.com/browse/109.167.128.234/Game/Dragon%20Age%20Origins%20v%201.01%20(RUS)/Update/DAO%20Content/DLC/The%20Stone%20Prisoner/DAO_PRC_OCP_2_1.0.dazip

I don't own Warden's Keep myself but that same site does seem to have a link to the offer file for it as well: http://filemare.com/browse/109.167.128.234/Game/Dragon%20Age%20Origins%20v%201.01%20(RUS)/Update/DAO%20Content/DLC/Warden's%20Keep/DAO_PRC_ONRX_1_1.0.dazip

I can only find links to "cracked" torrents for Return to Ostagar, but I don't know whether those would work, not to mention they're blatantly illegal.  It's possible  the .dazip from one of those torrents might work anyway since you legitimately have the rights to it so if you only download the offer file and not the "cracked" files you might be able to install it normally with daupdater.exe 

Currently I don't have any confirmed links to working files for that one.

I FOUND IT!!!!

Ignore the above. What you need to do is go to your User Entitlements page: https://social.bioware.com/user_entitlements.php

Assuming you've already registered your game you should see entries for all your DLC.

1. Next to the DLC you're missing the offer for, click "More Info - PC" (or "More Info - Mac" if you're using a Mac)
2. There will be two download links, one called "Content" and the other called "Offer." It sounds like your content files installed fine, so you just need to download the one called Offer. Repeat for each of your 3 DLC with missing offer files.
3. Use daupdater.exe to install the Offer dazips
4. Play your game and revel in the magically working DLC!

Hope this helps!