You can find them on many places in the Sirius Sector and on only very few places in other Sectors. Planets with the Mooring Fixture are all dockable Freelancer-vanilla planets (populated planets in Liberty, Rheinland, Kusari etc.), and three rather distant places which are Planet Earth in Sol, Planet Murmansk in Sovetskaya and Coalition HQ in the Vorkuta systems.
Mooring_Fixture is in Sirius Sector also available on big stations which have installed special mooring-fixture-module: as examples for bases types can serve Newark Station, Fort Bush, West Point Military Academy, Shinjuku Station, Aomori Station and ASF/CSF station in the X-3043 system. Exist are also handful small "special" stations with this module, which requires own exploration of the Sirius Sector. These small stations offers, for those who found them, purchase of the BMGs which are the best tradeable illegal goods (as example can serve one from small bases in the Hokkaido System).
Note_1: in the Crossfire mod are used two different types of mooring: first type is described above and second type is used for all military ships like are gunboats, cruisers, battleships and dreadnoughts (plus special Mining Ship), which can dock on all stations (included EVERY small station) in the Sirius Sector and on all planets with mooring-fixture.
Note_2: In multiplayer (MP) is at disposal, for official clans on the Server, possibility build clan bases with modular design. These bases also offers (on certain higher level) possibility dock for all (included big) ships types.
Warning!!!!: Is strongly advised to avoid docking big warships on "ship-base" types ... it is in some cases possible, but in some cases you can get stuck inside station-ship structure! The worst in this regard are Kusari ship-stations and liner-ship stations.