Isofix

[shervo]

They are not fitted to all, as above, was an option.

However, you can buy them separate or as a pair, I've bought a few in the past. Should be about £20 each approx.
Buy if you only have one kid, then I suggest just getting the longer section of the two for passenger side.

Unbolt rear seat, drill out metal covering, rivet in Isofix bracket and then bolt seats through it. Easy to do

Were can these be bought from? Was it second hand ones of ebay you have bought or brand new?