Not sure if one comes in the A1 seal pack or not. I don't think it does though. In which case, your best bet would be to contact Bob at www.fixmyangel.com
or Jay at www.pbsports.com
and see if they can scrounge one up for you - they don't have any listed at their respective websites.
If you can't find one anywhere, you can use a liquid gasket product from an automotive parts store to make one yourself using your current gasket as a template.