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 WHAT. Many of our members are interested in the achievements your company has made in.
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 we'll make everything convenient to the speaker.
Sincerely yours
NAME