As you can see in my signature, I owned an ALTEA my2006 before I bought a my2015 recently.
When giving away the old model, I saved some parts for retrofitting into the new one, like armrest, raised boot floor, space saver wheel and the parcel shelf (stowaway box) underneath the boot cover.
As the ALTEA facelift models come with a slightly different boot cover, the knob that formerly holds the parcel shelf (
pic#1) underneath the old boot cover (5P0 867 134 E/F) doesn't fit the new cover (5P0 867 134 G) any more.
Hence I had to construct some other fastening (
pic#2+3) to continue to use the old tray with the new boot cover.
In addition, the position of the two mountings attached to the tray (
pic#4) were sitting a little too far to each end and had to be moved a little inwards (~0,5cm each = as much as possible) to match the holders of the boot cover (mounting (5P0 867 575 A) + locking sleeve (5P5 868 767 A)).
Now the look and feel of the additional parcel shelf is back in my new ALTEA (
pic#5).
Hope that you are inspired or at least know now which part to look for ...
btw. I haven't seen pictures of a facelift ALTEA with this tray yet ...
EDIT: After reading your post over again, I reckon that you might only need those holders (mounting and sleeve) attached to the boot cover, they may be cheaper to buy at the dealers than to go for a used boot cover.