Does anyone know where I can buy a rear abs ring? Or do I have to buy a new bearing kit? Thanks

I have always thought that the ring was part of the wheel bearing, like the mk1, but apparently not.

Here is a link to a rear wheel sensor ring. I had to guess at your model and year as it is not in your profile.

 

https://www.ebay.co.uk/itm/MAGNETIC-ABS-RING-FOR-SKODA-OCTAVIA-SUPERB-YETI-04-15-REAR-/332275231682

 

Other suppliers too on the internet but as the cost is under £10, I suggest contacting your nearest TPS (VW group's own parts company https://tps.trade/) to get the correct part number for your vehicle or alternatively your nearest Skoda garage parts department..