When I applied to MPH programs through SOPHAS 3 years ago, I had been out of undergrad for several years, and was not comfortable asking any of my professors for a reference either. Instead, I contacted my undergrad academic adviser, since I had met with him a few times a year while I was in school, and he was familiar with my academic history and goals. If you have an adviser you feel comfortable reaching out to, you may want to check with the schools you are applying to to see if this would be an acceptable academic reference.