Reply to Inquiry and Inability to Offer Substitute
Your letter inquiring about [subject of inquiry], was brought to our attention.
While we manufacture a vast assortment of [products], none of our models fit the description you provided. We have never manufactured [subject of inquiry].
You may wish to direct an inquiry to the following distributor, whose firm has been in existence for many years and who may have the answer you are seeking:
[City, State, Zip]
We are sorry that we are unable to be of more assistance to you. Best of luck!