You'll be unlikely to find any in anything lke serviceable condition given how readily it absorbs water.
Also, if I recall correctly, it is fitted after the wiring and before the rest of the car and is a single piece that covers the front footwells, centre console and firewall.
So there's that
^^Why??^^
You don't know until you actually have a look in some breakers. I have 5 breakers - three of which live outside and have done for the last 5 years or so. None have wet footwells.
Because the foam is moulded to the shape of the floor pan and the wiring tray, when cut along the edge near to the transmission tunnel towards the join under the seat, and across forwards of the wiring tray, the profile of the floor pan holds it in place. The seat obvious needs removing to do it properly, but the seat mounting rails which form part of the floor pan more or less dictate its position when in place. A little bit of automotive spray adhesive doesn't go amiss along the cut joint.
It goes without saying that any cut through the rubber top surface and into the foam needs to be done with the sharpest of blades...
I little bit of thought and imagination goes a long way to finding a satisfactory solution to many problems - being negative is counterproductive