I've been doing quite a bit of research while trying to get SC3K Unlimited to run on Win7 x64 from it's original CD.
There are still a few sites that host custom content out there. I'm more interested in attaining all the official files Maxis released, but "custom content" could be included for a few of these websites.
Here's what I've found so far regarding updates and such
: Widescreen Patch https://www.gog.com/forum/simcity_series/simcity_3000_widescreen_patch_instructions Enable Additional Music Tracks https://www.gog.com/forum/simcity_series/sc3k_enabling_the_three_missing_music_tracks_howto_guide
There's an mp3 soundtrack linked in this post. I believe there's also a tool to convert WAV files to XA files which are used by SC3K. It would be possible to use an audio converter to convert the mp3 files to WAV format and then to XA for additional ('unreleased' hehe) tracks to use in-game.
Regarding Official and/or Custom Content
Note: I'm not sure what is included in the GOG version of SC3KU, but I've read in various places that you may need to upgrade the BAT (Building Architect Tool) system to a Landmark
(Maxis Official) Landmarks Package https://www.gog.com/forum/simcity_series/simcity_3000_unlimited_landmarks CityBuilders
(For all things SimCity. Includes Maxis Official Files from the old Downloads Exchange! Requires registration to download) https://city-builders.info
Here's a log of the creation of CityBuilders. Might be useful to look at old posts or links left in people's signature areas. http://www.sc4devotion.com/forums/index.php?topic=15853.0 SimCity 3000 Resource Center
(A bit dated, but hosts some interesting files) http://www.sc3000.com/files
Here's the link (via The Wayback Machine, courtesy of Archive.org) to the official Maxis SimCity Exchange
, though the files available for download are inaccessible due to the fact that you need to be a registered user in order to download any content there. But for old time's sake! (And for future [/past] reference)... http://web.archive.org/web/*/http://simcity3000unlimited.ea.com
I'll come back and update this post if I find anything else out there.
CityBuilders is probably your best bet for any official or custom content.