Gentlemen:
Our contract entered into on [date] specifies that we will deliver [specify goods] .
We regret to inform you that the goods herein referred to are unavailable because [set forth reason].
We are hereby requesting your authorization to subtitute the following product in lieu of the one we cannot obtain: [DESCRIBE] . If you are agreeable to this, would you please acknowledge your acceptance by letter.
We will look forward to your response.
