I posted about the same problem about the P800. Couldn't find matte and photo black for awhile, but then I could, so I'm good for awhile.
It's the chips. Each cartridge has that damn chip that communicates with the printer. Chips are in everything, and in very short supply. I just read that Ford is shipping vehicles with certain frivolous functions, like rear seat HVAC controls disabled, for now, just to get them in customer's hands.