I'm sorry to hear that you are experiencing issues with alerts. To start, are you currently monitoring the device the collector is installed on? If so, you can filter "Host Status" on the alerts page and the collector down alerts will populate. Alternatively, you can create a dynamic group for your collectors by leveraging "isCollectorDevice()" and filtering for that on the alerts page.
In terms of creating dependencies, there are currently two datasources that are mentioned on this page (below) that may be able to help.
Let me know if you have any further