If you need an extract which is not included on the downloads page, you can simply download the planet file and make your own extract.
npm install -g tilelive mbtiles
To create an extract the tilelive-copy utility is used. It takes a bounding box and a mbtiles file as input and ouputs the extract.
Replace the bounding box in the following command with your bounding box.
tilelive-copy \ --minzoom=0 --maxzoom=14 \ --bounds="5.9559,45.818,10.4921,47.8084" \ planet.mbtiles my-extract.mbtiles