So far I've had no luck finding a kit anywhere. I've hit some of the sites that specialize in marker o-rings kit but couldn't find one. I've emailed a couple of the sites, so far no reply.
I quickly checked out the listing of o-rings in the Ion kit listed above. It will give you most of the rings but not all. If you only need a specific o-ring check out page 19 of the EOS manual. After measuring a few o-rings and looking at SP part numbers I've found that you can determine what you need from the SP part number. For instance, SP part number ORN01790UR is a size 17 o-ring, 90 durometer and made of Urethane. With this info you can hit a local hardware store or order them separately online.