If you buy coolant form VW Group outlets, you should only be getting G12EVO now, I've just bought 12 litres, you can only buy it pre-mixed 50% and in 1litre containers - okay you can also buy 100 or 600litrs containers, but still all premixed.
I looked into buying conc G12EVO or the product from BASF that it in reality is, but so far no one in UK sells it and buying in from Germany adds enough to the price to make me forget that idea. Buying G12EVO from any VW Group dealership parts department costs £7.31 a litre, or is that £7.13, I've forgotten.
Currently there is no aftermarket supplier of that stuff, but I'm sure there will be in time when demand increases, aftermarket is still pushing G12 etc and G13.
Edit:- by the way, where did you find any reference to needing to replace VW Group coolant every 2 years?