all B6's have the anchor points, just not the Isofix hoops: just follow that link - it's £50-£80 and a 10min job to screw them in with a Torq screw... or about £750 from Audi.
If you've got the saloon: just lift the bench out
If you're still shopping for cars and can't figure out if it has one: the ones that had it factory fitted usually came with the front seat isofix too and had the button on the side of the glovebox to disable the passenger airbag.
I'd only recommend retro-fitting in the rear though!