The game has an addon, called Valkyrie, you can see pictures and information on mobygames, at the addon appears to be retail only, however there is an online store that sells it. The store itself is a little shady, no more than gamersgate though. The game is a digital download, but you have to use their client. To create an acount it asks the user for a phone number, which is unusual and raises some red flags. I wont link to the store, i'm not sure it is allowed. If you find the retail version of the addon, it will work only with the retail base game

I found it and archived it! Here ya go:

https://www.gog.com/forum/ascension_to_the_throne/valkyrie_ascension_to_the_throne_expansion