Downwind Marine (downwindmarine.com (619) 224-2733) in San Diego has this
material. If your ports use the stuff that I am familiar with, the seals
are hollow... almost like tubing. As such, O-ring material probably will
not work. If your material is solid, then you can buy material that is
used to make custom o-rings by the foot from Mcmaster-Carr (mcmaster.com
catalog page: 3234) It is called o-ring cord stock.

Hope this helps

David Braun
S/V Nausicaa