Literally in the exact same position. Emailed all of my previous bio professors yesterday. One emailed me back asking me to send in a personal statement/resume and we could meet early next week and he would write one. I haven't heard back from the other 3. I have a strong dentist letter and non science letter though.
If I never hear back from my other emails, I'll try to surprise them in their office. I guess I could get a current teacher to do one, but I don't know if that's frowned upon or not.