These guys are really good, but I've only used them to supply parts.
Volkswagen Transporter T6 Reversing Camera Retrofit
It's not cheap. You can buy the bits in the shop here.
Yeah thats the one i found, £850 fitted. I'm not that bothered but er indoors fancies one - her spatial awareness isn't the best!!
You can use aftermarket cameras just need to get the cable into the back of the headunit
I have been thinking about trying to make some adapter leads to allow phono plug cameras to connect to VW headunit
It goes into pins 6 and 12 on the rear of the connector and I have the crimp pins for those of required