But you do have at least one missile slot available for it to go into don't you? Remember that it's "pylon mounted" (as it was written before we had the selection keys available and it hasn't been upgraded yet), so you need at least one available pylon before it will be available for purchase (from tech 10+ planets).
I'll see about updating it to be key triggered and not pylon mounted, but that's a longer term job.
Alternatively, if you want to give yourself one, back-up your save game and then edit one of your pylon mounts to
"EQ_ARMOURY_MISSILEMACHINE_MINE". To do that search for the key <key>missile_roles</key> and in the array that follows, change one of them to <string>EQ_ARMOURY_MISSILEMACHINE_MINE</string>.Then save the edit, open Oolite and reload your modified save game. But do not use Windows Notepad to do this tweak (if you're on Windows), as it can add additional characters which screw things up.
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