I’ve used this wire to replace esc wiring. It is a bit more stiff than standard servo wire but does the job.

https://www.moddiy.com/products/Corsair-Style-3-Conductor-Flat-Ribbon-Cable-Wire-%2818AWG-Black%29.html

Hansen Hobbies sell a whole range of connectors and tools. If you want more flexible servo wire they sell black silicone wire, but only in single strands. They also have universal servo plugs.

http://www.hansenhobbies.com/products/connectors/servoconnectors/