Can I buy more storage for my iPad? Not cloud

You're welcome.

No, you can't. All iOS based devices are fixed at the amount of storage you bought when you bought it. If it's 16GB, it cannot be increased. If it's 32GB, it cannot be increased and so on.

The only way to get more space on your iPad is to delete things you don't need such as apps, videos, photos, text messages, email, files, etc.