I got my flywheel from a scrapped 2.5 156 V6 for £75. The standard GTA clutch kit then just bolts on.
60k miles later it is still light and smooth as silk - way better than the heavy DMF/standard clutch.
If you are going down that route then get a Q2 or Quaife LSD as well - these truly transform the handling - floor the throttle exiting a bend and take off as if on rails (negates the advantage claimed by TS owners - and I was one!) torque steer disappears.
I've still got some GTA flywheels left too, brand new original Alfa ones. Also a couple of original Alfa 3.0 solid flywheels from the 1996 GTV 3.0 24v before they switched to dual mass, these are balanced to the 3.0 crank and a kilo lighter at 7kg than a GTA flywheel, which is 8kg.