Keep a list handy with email addresses and contact information for committee chairs and board members.
Write job descriptions for all of the committee and volunteer opportunities, and make those descriptions available. Include amount of time involved, time of year the activity takes place, and whether volunteers can bring younger children with them.
Ask that space be set aside in each newsletter to thank volunteers or recruit new ones for upcoming events. Follow up with committee chairs to make sure they have reached out to all volunteers provided to them.
For large events, check with the high school to find students who can help out while they earn community service hours.
Split tasks into smaller chunks (e.g., setup, during event, and cleanup). Let people volunteer for the part that works best with their skills and schedule.
After an event is over, recap—see how many volunteers were actually needed, what kinds of jobs needed to be done, and what should be changed so that next time you will be able recruit and assign appropriately.