If you want to ensure that a specific dependency is downloaded from a custom URL rather than the Microsoft Store, you need to manage the deployment and distribution of that dependency yourself.
You should host the dependency file on a web server or a file storage service accessible via the custom URL will be like this:
"http://xxx/a/b/c/dependent1.appx."
Ensure that your installation or deployment script is designed to download the dependency.
You can use PowerShell to download the file from the URL. This script should be responsible for downloading and installing the dependency.