I know at one time there were additional premium modules available for NWN, beyond the Kingmaker modules that come with the Diamond addition (Wyvern Crown of Cormyr, Infinite Dungeons, Pirates of the Sword Coast, etc.), but it appears they are no longer available on the BioWare site (I get nothing but 404 errors on all premium module pages). Does anyone know if they are still available and if so, where can I find them?

Well that sucks. I didn't buy them before (when I should have), so hopefully GOG can strike a deal to start selling them here.

I am curious if anything has ever happened along these lines? I had Infinite Dungeons back in the day, but always hated it for that constant online checking that made it take forever to do stuff like saving and loading, including autosaves or something as I recall. If it's still possible to use my old CD keys it might get it to work, but the same problem would remain driving me insane, so I still really want to see it available on GoG DRM free somehow. (And honestly, I don't believe it's impossible by any means, but getting them to do it is tricky I won't deny.)

A lot happened in fact.
The installers became freely available. Then the authentication servers stopped working. Then started working again. Then were supposed to stop working.... and I'm not sure if they're working now or not.

The modules themselves are still downloadable from bioware:

http://content.bioware.com/neverwinternights/modules_premium/Kingmaker_Installer.exe
http://content.bioware.com/neverwinternights/modules_premium/ShadowGuardPlusWitchsWake_Installer.exe
http://content.bioware.com/neverwinternights/modules_premium/PiratesOfTheSwordCoast_Installer.exe
http://files.bioware.com/neverwinternights/modules_premium/InfiniteDungeons_Installer.exe
http://files.bioware.com/neverwinternights/modules_premium/WyvernCrown_Installer.exe

Probably someone who has NWN installed can test if they work or not.

They all work. I have recently completed a NWN gameplay period, including all of the premium modules.

They should be playable as long as they can connect to the internet...the servers were authenticating everyone at one point so you can try with the links above. I bought the originals so I can't check with out changing keys.

If you are disconnected from the internet then they still go to demo mode whether you bought them or not...

This doesn't work anymore, does anyone still have these somewhere?

See this post:

https://www.gog.com/forum/neverwinter_nights_series/other_premium_modules/post36