If your model is already hosted somewhere and is accessible via an API, you could have your space make an HTTP request to your model, as it’s done in the dalle-mini space. In that space they even their API URL with a secret.
Otherwise, you can have your space download the model at run time when the space starts up. In this space it’s done with torch.hub.download_url_to_file, for example, but you could do it with Python’s requests module or something similar. If you need to hide the URL that you’re downloading your model from, but still want to make the space public, you could use a secret for that.