Try This :
For Each tblRw As Control In selectSort.Controls
For Each tblCell As Control In tblRw.Controls
For Each ctl As Control In tblCell.Controls
Dim button As System.Web.UI.WebControls.Button = TryCast(ctl, System.Web.UI.WebControls.Button)
If button IsNot Nothing Then
If button.Text = btn_Filter1.Text Then
button.Visible = True
btn_Filter1.Visible = False
End If
End If
Next
Next
Next