Either store then when you create them in a list or array of RadioButtons (recommended) or you can find them via the Panel1.Controls array and iterate through:
For Each c As Control In panel1.Controls
Dim rb As RadioButton = TryCast(c, RadioButton)
If rb IsNot Nothing Then
If rb.Checked Then
Exit For
End If
End If
Next
If you chose the second option, I would put a distinctive value into the Tag property, or you will have to check the Text to tell which one it is.