Combine Destiny has been abandoned by its developer with the mention that it doesn't have free time to develop it further. Combine Destiny 2 was the long awaited sequel but it didn't see the light of the day as explained above.
However, you can download the installation package from the modDB, only that you need HalfLife 2 to be installed as well since this is the base for the mod and a replacement to the original game.
Use the following website to download the installation package: http://www.moddb.com/mods/combine-destiny/downloads
To install it, download the ZIP file and unpack it and then copy it over the HL2 directory.
