There are a few.
Gold Medal, they are the leading producer of flour in the US, under their brand as well as making many store brands, is not even making any flour until April 6.
The people that make Mission tortillas, which are very rare (at least in the western US) will be catching up shortly. They shut down for a mandatory cleaning every 2 weeks and their inventory maintains supply. Because of the demand surge that did not happen this time.
The toilet paper, paper towels, napkins shortage may last a while. The producers are concentrating on, at least for the company that employs me, 11 skus so there will not be the usual variety.