Now that's a tricky one.
here but they're out of stock. May know a source if you ask though.
You can get "2 x Chrome Plated Copper Tubes 490 mm Size OD 12mm 14mm 16mm watercooling" but it's hard and not recommended for bending as the chrome is likely to flake off.
Looks like it may be available in European countries. Spain apparently use it....that's all I could find in the time.
The Chrome coated is mad over priced, actually I already have a quote to chrome a few meters of copper tube - you can also get black chrome and nickel/black nickel so possible - but you bend it then get it done when its already shaped. I'm gonna have a look around but ultimately i'm sending the case back Thursday probably so can't do anything... What i'll probably do is fit the PETG and then if I go copper just drain and replicate the bends like for like and re-fit. We shall see, a bunch of sleeving arrived today so i'll just no life fully braiding all my cables and learning to use sketchup for some custom stuff.