SC4 base files are re-distributable...
"All add-ons based on spacecraft4.dll may be distributed freely with this base pack
included but you should preferably ask to download last spacecraft4 version"
I feel tempted to create a basic satellite add-on and upload it named "Vinka's spacecraft demo"... that way people can find spacecraft.dll on OH.
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Did just that!
https://www.orbithangar.com/searchid.php?ID=7108
For some reason there's no corresponding discussion thread for that add-on, but really, it's just a simple cubesat setup with spacecraft4 along with the entire SC4 package.
Should be useful specially for new members.