Dear (Title of the person you are addressing the letter)
Thank you for inquiring about our [mention the name/code of the equipment] I am enclosing a copy of our catalog for your perusal through fax.
It has been our four years of intensive research efforts which finally saw the light of the day when we succeeded in developing [mention the name/code of the equipment] to provide educators a perfect, comprehensive and effective means of sending information and thus modernize educational methods. We are of the belief that children are immensely receptive and stimulated in their quest to learn through a means which has the usage of audio-visual material.
We will be happy to receive your comments after you have done the review of our material. We shall be pleased to answer [tell the client you are ready to listen], if any.
Thanking you once again for your interest in the [mention the name/code of the equipment]
[Mention your name]