first time you may write as follow:
Dear XXX,
    How are you ?Wish everything well with you and your esteemed company !
    We are in receipt of your letter dated Aug 10 ,and as requested was expressed you 3 catalogues for our refrigeration goods .We hope they will reach you in bue course and will help you in making your selection .
    Wish we will promtoe business as well as friendship!
    Best wishes !


no any returns u still may write agian like this:
Dear XXXr,
    Good morning! Hope you have got a wonderful weekend!
    For several days no news from you, my friend. Now I am writing for reminding you about our offer for item of **** dated ** ** ** according to your relative inquiry. Have you got (or checked) the prices or not? ( You can add some words to introduce your advantage of your product or something else to attract the customer). Any comments by return will be much appreciated. It will be our big pleasure if we have opportunities to be on severice of you in near future.
    Looking forward to your prompt response,
    Thanks and best regards,
    Yours Faithfully

If still no any response, you can write another one about one or two month later:
    Dear XXX,
    How are you? Hope everything is ok with you all along.
    Now I am writing for keeping in touch with you for further business. If any new inquiry, welcome here and I will try my best to satisfy you well with comptetitive prices as per your request.
    By the way, how about your order (or business) with item ***? If still pending I would like to offer our latest prices to promote an opportunity to cooperate with each other.
    Thanks and best regards


   wish you good luck bro!