Sandbaggers EAW Tally-Ho! has long been a definitive source of alternate files for EAW, many many planes, theatres and campaigns, terrains, speech, and most other things.

All the files on this site are useable with the GOG version of EAW.

thatoneplease.co/Tally-Ho/NF128C.html

Sadly, getting Error 404

Here is the right link

https://www.thatoneplease.co/TallyHo

Edit.
The GoG version uses the old file-management system. You copy the files and paste them into the root folder.
To undo this you have to find the files in the root folder and delete them. This is a PITA- it is easy to make a mistake and wreck your system.

The OAW file-manager makes life much easier and I made a version for the GoG install.
Check the "Expansion of your GoG EAW installation" thread (June 7th 2021) for more information.

Here is a link to an extensive download

https://drive.google.com/file/d/1zuauDN_275g0QItPcEXvDvJgVAXBJDji/view?usp=share_link

The downloaded installer will create a "1.28c_2022" folder. It has the new exes in it, a simple file manager and several theatres: