Dear sir/madam:
[organization] would very much like to have someone from your company speak at our conference on [topic].
As you may be aware, the mission of our association is to promote [products]. Many of our members are interested in the achievements your company has made in [areas].
Enclosed is our preliminary schedule for the conference which will be reviewed in weeks. I'll call you [date] to see who from your company would be willing to speak to us. I can assure you that well make everything convenient to the speaker.
Sincerely yours,
[name]
[title]