Searching for stainless steel brake lines I found Probrake out of Germany. The page is wonky and you almost have to update to English on every page (unless you read German in which case you don't need to do that!)

Arrived very quickly - very high quality - can configure the color of the lines, too. I think it only took like 3 days to get them

Just throwing it out there for anyone looking to upgrade. Mine seemed fine but at 25 ish years old I'd rather spend the money when I don't have to than suffer the consequences if they failed.