Where can you buy a new circuit board for a mosquito magnet defender?

You can not buy them. Authorized dealers are the only people who have access to them and they will not sell them to the public... They want you to send the entire unit in for repair. You might want to check out http://urefillit.com. I believe he repairs circut boards and, if he can not, there is no charge. I purchased his trouble shooting & repair guide and that is all it took>> No parts were needed afterall.... as I originally thought! Good luck!