Most likely those predate the Downloads Database, which dates from 2006, after Civ IV's release. While some items from before that time are in the Downloads Database (either uploaded by their original author or by someone else later on), many are not. But their original threads should still be in the forums. Whether the attachments for the items still work is a case-by-case question - generally they should if they were uploaded to CFC (except for a gap in the 2007 - 2008 range), but it's unlikely if they were uploaded to third-party sites, due to bit rot over 20 years on the Internet.
As for Goldflash's Altered Tech Tree Mod?
I found it. Download still works too. Only catch is that it's a .ace file, which hardly anything supports these days.
PeaZip supports it with an optional plugin,
as described here, and perhaps you still have an old copy of WinAce? I think I do from my archival work a couple of years ago, on my desktop - if so I can re-package it to a more modern format, and perhaps add WinAce to the Utilities section as the only sites I see it now are filled with faux download buttons if viewed without an ad blocker, and thus I cannot in good conscious link to them as the rate of clicking a bad download button rather than the real one is very high.
I may be able to help locate some of the others as well, once I find some dinner. Uploading them to the database when you find them is also acceptable, with a link to the original thread, and I can reassign them to their original authors. The main reason it hasn't been done is that it is a lot of work to add five years' worth of pre-Downloads Database items to the database, especially since there was a lot created during that time. But who is GATTM? Either I'm forgetting the acronym of that was before my time.