KitchenSavvy has the substitution for canned evaporated milk and sugar for sweetened condensed milk:

For each cup of condensed milk, use 5 fluid ounces of evaporated milk and ¾ of a cup of granulated sugar. Heat the evaporated milk and sugar together over medium heat until the sugar is dissolved completely. If your recipe says to warm the condensed milk, cool it to the desired temperature, otherwise cool to room temperature before proceeding.