Proper flaring tools for OEM-equivalent laminate steel brake pipe are several hundred quid, plus VW were the only source of the correct lines that I could find in the UK.
I settled for copper-nickel (also known as cupro-nickel, kunifer, cunifer) lines made up by Automec as I was replacing the whole lot. Was £125 for the lot and saved me the hassle of flaring them myself. The copper-nickel is a bit stiffer than straight copper, so doesn't kink as easily and is better to bend by hand.
In the past I've flared bog standard copper ones to replace the rear lines, and never managed a hugely neat job.