Ben,
The cable is still (actually again) available from Neumann. But it's expensive.
No original Neumann tube mic supplies are made anymore, save for the ones used in the company's hybrids, M147, M149, etc.
But there are a couple of first rate power supply manufacturers around which can provide first rate, clean, filtered and stable DC output. (I won't mention names because I am affiliated with one of them.)
You will need to provide the 12-pin female chassis-mount Tuchel connector, though. Again, no biggie: on German eBay, you can get them at reasonable prices.
Best of luck,
KH