Limit of 10 injectors per ship?
are the other 9 purchasable, unlockable, rewarded or shared?

There is only ever 1 injector, omicron injector, unlocked and placed into your ship near the beginning of the game.

then what is the purpose of the "ship limit: 10 injectors"?
are their other types of injectors? (not necessarily Omnicron)

I don't about the limit 10 thing, i think webguydan willl change it.

at present its a highlander part (there can be only one)
not sure if the 10 limit was a misprint or if the door has been left ajar for more to be added in a high level mission.

The limit of 10 was never removed from when the game was in it's early developement stages. You can only have one 'injector'