Chassis repair sections are available from the usual places, but that looks like it could be repaired much more cheaply and quickly by cutting out and welding in tbh.
Thanks might go with a panel as i found its a pain getting a nice bend in the thick metal Can you replace them without taking the cab floor up.
You might have to drill out the spots in the floor panel, but should be do'able. I did it, but my floor was messed up anyway.
The floor may not still be attached to those chassis legs Mine has popped off with mud and rot on top of the legs.