Finding Negrini-specific parts is nearly impossible, but I've found that most parts are common to other brands.
For instance...I needed control levers. You're not going to find Negrini controls, but many bikes used the Magura-brand controls. Most electrics on our mopeds are made by CEV, and they are widely used.
Most of my troubles have come from rebuilding my motor. Again this motor is not specific to Negrini mopeds. It is a Morini Franco MO-2 and it and other motors similar to it were used on many different mopeds.
I am about to order a fuel petcock from Mr Moped. They have a listing for a Morini petcock that sounds like it will fit my moped.
What parts are you looking for?