I have never seen any.

If a child as their own flight seat they can take their own.

We are going to Spain later today and will be taking our own booster seats.

Update.
We have just got back from Costa del sol and a lot of people were taking their own baby and booster seats with them on the planes.

Hi, my niece is flying to Malaga next week with a 4 month old baby and is unsure whether the airport taxis will have babyseats. Does anybody know if the taxis outside the airport carry babyseats or will she have to prebook with a private taxi company.Thanks Helen