Found this out awhile ago and felt it might help others who weren't aware.
Here's an example to illustrate the method:
This is a link to the Green Shift gamemode: garrysmod.org/downloads/?a=view&id=126491
This is the link to the Green Shift download: files.garrysmod.org/126491.zip
As you can see the id value 126491 is the name of the download.
So as long as you have the id, which can be found in the address bar of your browser while viewing a garrysmod.org page, you can download corresponding files.
You should use this trick until Garry fixes it.
Here's an example to illustrate the method:
This is a link to the Green Shift gamemode: garrysmod.org/downloads/?a=view&id=126491
This is the link to the Green Shift download: files.garrysmod.org/126491.zip
As you can see the id value 126491 is the name of the download.
So as long as you have the id, which can be found in the address bar of your browser while viewing a garrysmod.org page, you can download corresponding files.
You should use this trick until Garry fixes it.