For those of you still looking for an 11 or 12 tooth sprocket, I have a few leads. Yesterday i ordered 1 12 tooth for a Honda CBR 600 f4i (520 chain) from Sprocket Specialists. They let me order just 1, but it was their last. However, they are doing small runs now of 11 and 12 tooth sprockets and so as I understand it, if you order at the right time there is no minimum order quantity, and they only charge $34.99 with a 10% discount for FSAE. Their website: www.sprocketspecialists.com
Additionally, Thrust Sprockets will do custom orders, but have a minimum order quantity of 5 sprocketswith a lead time of a couple of weeks. However, their price is only $23 each for five, so you can afford to buy five and sell the rest to other teams. Their website:
www.thrustcompany.com

Also, I have found a company that makes great rear sprockets. Sidewinder Sprockets made us a custom rear sprocket blank that we milled our own hole pattern in. And it only took a week to get here after we ordered. They are a little pricey, but they claim to have the best quality out there. I asked them about custom front sprockets, but they said they couldn't do anything less than 13 for the Honda.Their website: www.sidewindersprockets.com