Retrieve data across all site collections

I am attempting to create a web part similar to how the News webpart works but with more requirements around what shows on the hub or main site collections. I am really looking for examples on how to aggregate data into my web part but can't find good code samples on how to do so. I've found samples on how to get data from a single specific site collection, but i'm trying to figure out how to do it with multiple site collections. 

Does anyone know any examples that you could point me to?