Variable Scoping On Codebehind In C#?

I have an asp.net page (C# codebehind), and in page_load there are various linq queries returning anonymous types, such as:

var customersAdded = from r in AddedRecords
select new { Ref = r.CustomerRef, Name = r.Customer_Name };

On the page I have a button called 'export to excel', and in that buttonClick event I try to refer to customersAdded. It says it doesn't exist in the context. I know I've overcome similar issues in the past using things along the lines of:

if (File.Exists(System.Web.HttpContext.Current.Server.MapPath("~/App_Variants/" + GetUserTheme().ToString() + "/images/" + i.ImageUrl)))

So question is, how to refer to the variable? And for reference, if I say wanted to refer to a value in a control (eg a textbox on the page) would the same or different approach apply?