You don't say if your vehicle is a PFL or FL mk3 so I'm assuming PFL as you already have rear sensors and camera as the FL can't have rear camera without front sensors. You have options and can source the parts yourself from
Car-Systems or other suppliers and if you're confidant perform the retrofit yourself and then get them coded by someone with access to VCDS. Your other option is to contact a retrofitter who will supply/install/activate the front sensors for you. There are site sponsors who are retrofitters who will be able to assist you so drop a PM to
@DJAlix who runs
VAG Car Coding as I used his Leicester based partner to complete my retrofits who comes highly recommended.