slant six distributor o rings

Hello everyone! I got hold of an NOS Mopar Performance electronic ignition system and am finally getting around to installing it. The distributor only came with one o ring...the bigger one than goes right under the mounting plate. I'm looking for the one that goes around the housing that fits into the block. NO ONE seems to have ANYTHING that will fit! Do you guys have a source I may go to that will be able to help me with this little problem?
Thanks!!