dear sir/madam:
thank you for your letter of [date].
im glad that you are also going to [place] next month. it would be a great pleasure to meet you at the[exhibition/trade fair]. our company is having a reception at [hotel] on the evening of [date] and i would be very pleased if you could attend.
i look forward to hearing from you soon.
yours sincerely,
[name] [title]