Oh, yeah, this is a major pain in the a**. So they want proof from a doctor/midwife/np that you were pregnant. I up'd from the first trimester on but saw a chiropractor. My chiropractor filled out my form, signing it and sticking in her licence number. Any form that is a pregnancy verification from a medical professional with your due date should surfice.
In the event you don't have any of these forms, you'll have to see a doctor to write a verification that you were pregnant via postpartum interview/exam/whatever they want to give you the darn form. So, my advice, find a community health center to do it.
You might want to call the person in charge of homebirths at the county to see if you can bring in your UP records or photos to verify the pregnancy and save yourself the trouble of having to go to the doctor. I'm in northern California but getting the BC was such a pain! I hope it's easier for you! Congratulation on the birth!!!!