You can try ESA third party portal where you can find detailed information and related redirecting for accessing data. In order to download IKONOS (https://earth.esa.int/web/guest/missions/3rd-party-missions/current-missions/ikonos-2) imagery you need fast registration (approx. 2 days) but for QuickBird (https://earth.esa.int/web/guest/missions/3rd-party-missions/current-missions/quickbird) you need an approval of project proposal (approx. 2 weeks).