One left, searched with a zero in front and found it, $6.97 w/shipping. Or use the cover plate as a template and make one from rubber/cork gasket material.
https://www.ebay.com/itm/T36-Evinrude-Johnson-OMC-0305299-Gasket-OEM-New-Factory-Boat-Parts/312345512046?epid=1550238919&hash=item48b93e486e:g:ussAAOSwB9FcAN2Z
