Comcast will carry NBC Soccer Olympics but only if you pay for it.
At least that is what it looks like.
There are lots of entities that are going to make money on the Olympics and NBC is a big one. I liked the plan of taping and showing live and delayed broadcasts of all the Olympic soccer. I think NBC will make a pretty penny off of it. But it looks like Comcast and a few other cable operators no doubt, want to make some money too. So they will put the NBC Olympic Soccer behind a pay wall. For a roughly two week competition, I don't want to have to pay for at least a month's worth of programming (or more-Comcast doesn't have a sense of humor about buying programming for just a month).
As Laurie said, start calling and emailing.