Dear

After checking with all of our other stores in the area, I regret to inform you that I have been unable to locate another [item requested] for you.

If you would like me to place a special order, I would be most happy to do so.  Normally, it takes between four to six weeks to receive merchandise ordered in this manner. If this is your desire, please call me at your convenience at [telephone and extension].

On behalf of  [name of firm]  I would like to thank you for shopping at our store and if there is any way that we can be of further assistance to you, please let us know.