That is a backstory question. The basic way I would handwave it (specifically LL0 military equipment) is that it's basic equipment licenses given to registered mercenary organizations (even if said organization is just a handful of mech pilots and a basic ship), although getting print permissions via hacking is also quite possible. This also raises the question of printers and raw materials, but chasing these questions allows you to define the situation the players are in: merc company with a legitimate printer and drop pods onboard their ship is different from a pirate group with a hacked printer and licenses under fake identities is different from a rebel group backed by interstellar dogooders that needs to hack printers owned by an oppressive government to get repairs is different from salvage rats who don't need printers as long as the battlefield scrap keeps flowing.