broken screen of MacBook Pro (Retina, 15-inch, Late 2013). Where I can find the part?

Try iFixit.com and Powerbookmedic.com.

Ciao.

It's not likely parts are available as yet outside of Apple. If you do the replacement yourself then you will forfeit any future Apple support. I suggest you take it in to the local Apple Store and let them fix it for you.

Apple does not sell replacement parts, any you find will be third-party knockoffs. Take your Retina to an Apple store genius bar and have the techs tell you what needs to be done. New Retina screens are not cheap, they normally replace the entire lid as a unit.