If you need a custom nipple, there's a reputable custom nipple manufacturer named Blomquist Percussion Works in Indianapolis, IN that can make them.
The problem is that his website has been down for a long time, and prior to that his website had the wrong phone number and email address.
So now he has probably let his website lapse.
He is still in business making nipples, but there have been different phone numbers reported to contact him.
The last one that was reported is confirmed to still be one of his by reverse lookup as of today.
317-706-0712 reported on 7/18/11