I’m not sure I follow what “that” issue is when you talk about data binding.
What’s the issue with using 3 radio buttons? I’m assuming you are trying to control one field correct? If silver needs to be null, I think you can make that a value of a radio button. Then a clever arrangement on the UI can make the default choice clear. You could also make a button to clear the value. They would both be empty then.
If you are dealing with more than one field, and you are having trouble when you data binding, you could probably do the setting yourself. You would set the correct state of the check boxes on load, then when you check the boxes, set the value(s?) in the data view within the code blocks shown above. I’m not sure what problem you are having, but maybe adding a layer of separation would help?