No worries!
In the past I have asked our president, advisor, etc to be a reference. I'm sure that they will be happy to vouch for your credability even if they are at convention.
I have had to do the same thing before by listing someone then asking them after the fact. Find two good references and let them know you will list them and notify them if you do sumit their contact info to anyone
It's kind of like the girl scout motto: "Always be prepared"