How to implement an NoC (Network on Chip) in my DE1-SOC (Nios-II, Qsys)?

100 cores of what?

Nios relies on the Avalon Bus - usually with the Nios acting as the master and other units connected via a memory mapped avalon interface.

This way you can have any existing IP or any other IP you chose to design yourself (as avalon is a straight forward interface, very similar to AXI).

NoC is usually a term used for Asic, not FPGA.