Nate, this place should have it.
Marco Rubber and Plastics
334 Clark Street
North Andover, MA 01845
P: (978) 688-3500
F: (978) 688-6915 www.marcorubber.com
That place was amazing. Any size/shape/thickness gasket you want, and they no charge for the few I needed. An unimaginable collection. Stacks and stacks of bins. A warehouse with nothing but o-rings. Oddly cool.