I see I'm not the only one who was thinking about it. But 3D printing technology seems like a valid answer. If not, it would look like a Darth Vader suit was a common life support suit in the galaxy, thus Vader wasn't the only one wearing it...
It seems a bit un- Star Warsy,...more of a Star Trek replicator answer
Really Lucas just wanted us to see Darth Vader complete,....through the OT we saw the Vader costume evolve from a steel grey/black weathered costume to a high gloss costume,...Lucas was very proud that the ROTS costume was at last perfect,...symmetrical, he was fixing, once again imperfections of the OT, imperfections that probably only annoy him
Ideally the cybernetic Vader should have been more wires & exposed bionics,.....rather like the Episode 1 3PO,....his respirator breathing for him would be the only recognisable Vader connection
By the time we see him in the Rebels cartoon,....(which they have decided to base his costume closer to the RMQ design),....he's looking like what he does in the OT
If he's in Rogue One,....it would be nice if they don't use the 'perfect' ROTS costume & have him in the duller more metallic ANH style
So many things were wrong with the Prequels,....missed opportunities
J