Granted, there is a non-vanilla added lvl 10 turret in Crossfire, but IMHO, the guns is where it's at. I will say however the lvl 9 Buckshot and lvl 9 Skyblast B turrets are great vanilla turrets.
FWIW, Crossfire adds about roughly 9 new lvl 10 guns, some of which are much more powerful and useful over vanilla guns and especially the turrets. (I do hope OP will address this someday, I see some Crossfire alien species who use their own make of turret which would be nice for turret equipped ships to have and level the playing field in this regard against very heavy fighters IMHO)
Regardless, to help you in your journey in procuring the best turrets Daynox, here are some hints.... You will have find them, you cannot buy them and you won't find them in the Sirius sector. 

Good journey Daynox and good hunting sir! 