Contact Marriott group or corporate sales.

https://www.marriott.com/meetings/gr...l-discounts.mi

You will likely be asked to enroll with a corporate TA which handles group events. This is especially true if the business will pay for the rooms on a master account and thus the business will either accumulate rewards or take advantage of specialized discounts offered for doing this. Won't make employees overly happy, but the savings can be fairly decent.