Sounds very much like you will have to start over.
If you did not save them to the cloud either by the automatic upload or manually uploading, then you have lost them.
If you can get access to the Slim, then you might have a chance of getting them back.
Trouble is, if you did sell it, then you would have defaulted the console back to basics. (as it came out of the box) and it will be gone anyways. The current owner may have done the same if you did not.