Well blow me.. All I could find when I was looking was the load space, same as you it just wasn't enough, it needed to cover the floor under the seats for when the dogs get in stinking wet from a walk.
I bought a roll of rubber matting and cut to shape, had enough to put under the bottom part of the rear seat cover so that when you put the seats up it covers the underside of the seat. I'll get a picture later if I remember. Costs ALOT less too but requires a bit of time and effort but not too much.
A full roll of 140mm x 1000mm cost about £70-£90 and you could do two cars with that. I looked around a nd found a fella selling nearly 6m and had it off him for a £10 RESULT