CompUSA's are suppose to have the upgrade cd's. Doesn't mean the will or will have it available in a timely fassion, but they should have it. I also hope Fry's electronics has it. Any other authorized Apple reseller should have it from what I have heard, but then again I have heard reports that certain stores arn't carrying it for some reason.
My CompUSA has a full time OFFICIAL Apple Rep in the store. She told me that Apple was trying to integrate the Apple Store within some CompUSA's. I haven't talked to her since the announcement about 10.1 but I'm almost certain about my CompUSA carrying it on Saturday morning. I tried calling her earlier today about this but she was on her lunch break so I guess I'll try later or just wait 2 days and see what happens.
I ltalked to my local compUSA in San Rafael. They were not going to carry the upgrade. He called Apple and he said that they would make it available as a donwloadable online. It didn't seems like the guy knew what he was talking about so I didn't really trust his judgement.
I later called Apple myself and they said that almost all Circuit City stores will carry the upgrade.