Dear Bookstore Rep #2,
In response to the out-of-office auto-reply I received from Bookstore Rep #1, I am forwarding my book order to you (as per the instructions in the autoreply).
From Bookstore Rep #1
I will be out of the office until [date] please forward orders to Bookstore Rep #2
To Bookstore Rep #1
Dear Bookstore Rep #1,
I need to place an order for # copies of [textbook] by [author] ([edition] [ISBN]) for [course number].
What Bookstore Rep #2 wrote back:
You can place an order with me by e-mailing me the title of your book, course number and number of copies.
-Bookstore Rep #2