This may not be the right forum to specifically address your question real time.

Sorry to hear about the missing/lost passport. It is frustrating!

To get Chinese visa in one day may require you to submit all the required documents before certain time deadline.

There are third party services providers that charge you a service fee to get visa in one day but I am not based in SFO to know who they are.

You may explain to UA the situation and sometimes you may get your change fee waived to get on a flight at a later date when you are able to secure your visa. This may be better than doing SDC.

You can definitely get visa in a few hours in Hong Kong but that require rerouting and even overnight, so may not be practical for you.

moondog, FT member with more China travel experience than anyone I know, may have more to share. Perhaps PM him for advise.