You don't really need a form. What you need is to stop doing this :-).
Seriously, the School should conduct these events and pay the bills. If an individual wishes to underwrite the costs, they can write you a check.
Absent that, no form is needed as much as a copy of all the receipts and proof of who paid the bills (canceled check or credit card receipt. Then, you need to verify the expenditures were appropriate and determine who paid the bill. You then issue a GIK receipt to that individual(s), but without mentioning any dollar amount.
A third option is to reimburse the individuals for their costs, and then they can write you a check.
John
John H. Taylor
Principal
John H. Taylor Consulting, LLC
2604 Sevier St.
Durham, NC 27705
919.816.5903 (cell/text)
Serving the Advancement Community Since 1987