Have a look at this pic and see if you can work out which number it is.
Let me know and I'll see if there's a non-army part number for it.
Greg.
Edit. If it is the part labelled as 3 in the pic, they called it "Tunnel Mat, Floor Rubber, Rectangular, Black, Transmission.
Seems to be part number MUC1253. Landybitz is selling them on eBay.