MANY "bed turret" rigs were built by third-party suppliers, then adapted to any lathe where there was a pressing need. That is bound to have been done at least a few times, but would not have needed "factory" blessing. All it takes is an accurately milled and fitted adapter plate and clamp.
With the Graziano's unusual bedways, if you chase that, you would probably need a size more commonly fitted to a lathe with lesser swing. Otherwise, socket centerlines could be difficult to lower by enough for spindle-axis alignment?
Mine, for the 10EE, is a used-but-good Enco "hex" turret that may have once graced a South Bend? The 5/8" sockets fit a wide choice of once-common Hardinge tooling readily available, used market.
Monarch also had more than one type of their own. Not known to me if they actually made some, ALL, or none of those or bought them in from the speciality makers.
In Europe, Graziano may have had the same situation?
IF. OTOH, you refer to Morse-taper-mounted "turrets" rather than "bed" turrets?
Some might consider those a waste of time as well as money?
Probably buy (or be given) half a dozen Ward capstans for the price of a Graziano tailstock turret....if such a beast exists...which is very doubtful. Have seen Chinese ones offered in morse 3, if you insist on something along those lines.