I havn't done the diff yet so havn't bothered to chase up a clutch kit, but you can buy lightened flywheels from ktec etc or simply get any good machining shop to lighten & balance an oem flywheel to your spec.
I think you already fitted the lightened pulley too from memory ?.
Just a small word of warning to keep in mind...
Lightening rotating mass is all well & good up to a point but if you go too far you can run the risk of losing significant engine braking which is fine on a race car but undesirable on a road car (rotary engines suffer from this due to the lack of inertia hence why they also rev so freely).