I realize your request is a year old now, I am new to the website... It may be too late, your son may be in public school by now - but there is one preschool/elementary I know of that is geared towards "troubled" kids. I checked it out for my daughter when her preschool threatened to kick her out. It is called "Spatula Soup". I was able to work with her preschool and keep them from kicking her out - she made it through Kindergarten and then transitioned to public school.
Other advice I can give, after spending the last 8 years trying to get adequate help for my daughter... Her diagnosis is bipolar disorder, obsessive-compulsive disorder and ADHD. Be very careful that you are only dealing with ADHD, and not something more. Many doctors dismiss the other disorders, saying children don't have them - even though they are genetic... I tried Herbal, Naturapathic, Homeopathic, diet/supplements, to help my daughter before I resorted to pharmacological. Only the medications have helped. Don't fear them or feel like less of a mom if you choose to use medication. These disorders are brain-chemistry issues. Introducing chemicals to balance the brain out, may be the only answer. The other ways are maybe 30% effective, that means the other 70% of people won't be helped with these "natural" choices...
Keep on top of your school. If you can't afford a private school - most of us can't... stay in the public school system. The State regulates the special education and can be a big help if your local school or district fights you. It took me five years to get an IEP for my daughter. Contact the state special education department and find out all your rights.
Good luck, I know what you are going through.