How do I get a value from by gridview in C#

I have a web page with a list of divisions in a gridview. I have a separate area on the page that allows the user to enter a division and when the user clicks on the Add to Grid button, it needs to check if the division already exists and display a message to the user.

From everything that I have read, I should be able to do the following but it is not working.  tb is returning null yet it works in my RowUpdating event.  Any help is greatly appreciated!

Here is the code that I am trying to get to work:

                Boolean unique = true;
                TextBox tb;
                // Validate the Division doesn't already exist
                foreach (GridViewRow row in gvDivisions.Rows)
                {

                    tb = row.FindControl("tbEdit") as TextBox;
                    if (tbDivision.Text.ToUpper() == tb.Text.ToUpper())
                    {
                        unique = false;
                        break;
                    }
                }

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This code in my gridView_RowUpdating event works:

                // UPdate the values in the datatable
                GridViewRow row = gvDivisions.Rows[e.RowIndex];
                // get currently selected value
                TextBox tb = gvDivisions.Rows[e.RowIndex].FindControl("tbEdit") as TextBox;
                dtDivision.Rows[row.DataItemIndex]["Division"] = tb.Text.ToUpper();
                DropDownList ddl = gvDivisions.Rows[e.RowIndex].FindControl("ddlStatus") as DropDownList;
                dtDivision.Rows[row.DataItemIndex]["ActiveStatusFlag"] = ddl.SelectedValue;

                // Reset the edit index
                gvDivisions.EditIndex = -1;

                // Bind the data
                gvDivisions.DataSource = dtDivision;
                gvDivisions.DataBind();

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Here is my gridview markup:

            <asp:GridView ID="gvDivisions" runat="server" CellPadding="5" 
                OnPageIndexChanging="gvDivisions_PageIndexChanging" OnRowCancelingEdit="gvDivisions_RowCancelingEdit"
                OnRowEditing="gvDivisions_RowEditing" OnRowUpdating="gvDivisions_RowUpdating"
                AlternatingRowStyle-BackColor="#0099CC" AlternatingRowStyle-BorderColor="Black" 
                AlternatingRowStyle-BorderStyle="Solid" AlternatingRowStyle-ForeColor="White" 
                AlternatingRowStyle-HorizontalAlign="Left" AlternatingRowStyle-VerticalAlign="Middle" 
                BorderStyle="Solid" HeaderStyle-BackColor="Silver" BorderColor="Black" 
                HeaderStyle-BorderColor="Black" HeaderStyle-BorderStyle="Solid" 
                HeaderStyle-HorizontalAlign="Center" HeaderStyle-VerticalAlign="Middle" 
                HorizontalAlign="Left" RowStyle-BorderColor="Black" RowStyle-BorderStyle="Solid" 
                RowStyle-HorizontalAlign="Left" RowStyle-VerticalAlign="Middle" 
                AutoGenerateColumns="False" 
                AutoGenerateEditButton="True"
                EmptyDataText="No Divisions Found" AllowPaging="True">
                <AlternatingRowStyle HorizontalAlign="Left" VerticalAlign="Middle" BackColor="#0099CC" BorderColor="Black" 
                    BorderStyle="Solid" ForeColor="White"></AlternatingRowStyle>
                <HeaderStyle HorizontalAlign="Center" VerticalAlign="Middle" BackColor="Silver" BorderColor="Black" 
                    BorderStyle="Solid"></HeaderStyle>
                <RowStyle HorizontalAlign="Left" VerticalAlign="Middle" BorderColor="Black" BorderStyle="Solid"></RowStyle>
                <Columns>
                    <asp:BoundField DataField="DivisionID" HeaderText="ID" ReadOnly="true" />
                    <asp:TemplateField HeaderText="Division">
                        <EditItemTemplate>
                            <asp:TextBox ID="tbEdit" runat="server" ToolTip="Division" Text='<%# Bind("Division") %>'
                                CssClass="TextBoxFormat" MaxLength="30"></asp:TextBox>
                            <asp:RequiredFieldValidator ID="tbDivisionRequiredFieldValidator2" runat="server" 
                                ErrorMessage="Division is required" BackColor="Red" Font-Bold="True" ForeColor="White"
                                ControlToValidate="tbEdit" Display="Dynamic" validationgroup="Info"
                                Text="*"></asp:RequiredFieldValidator>
                        </EditItemTemplate>
                        <ItemTemplate>
                            <asp:Label ID="lblDivision" runat="server" Text='<%# Bind("Division") %>'></asp:Label>                       
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:TemplateField HeaderText="Active">
                        <EditItemTemplate>
                            <asp:DropDownList ID="ddlStatus" runat="server">
                                <asp:ListItem Value="Y">ACTIVE</asp:ListItem>
                                <asp:ListItem Value="N">INACTIVE</asp:ListItem>
                            </asp:DropDownList>
                        </EditItemTemplate>
                        <ItemTemplate>
                            <asp:Label ID="lblActiveFlag" runat="server" Text='<%# Bind("ActiveStatusFlag") %>'></asp:Label>
                        </ItemTemplate>
                    </asp:TemplateField>
                </Columns>
            </asp:GridView>

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