I'm in Europe - maybe that makes a difference? The Walther website has barrels listed under the accessories tab for the premium models - Expert & Anatomic https://www.carl-walther.com/sport/products/p/2773121I wasn't sure the Blacktec could be had with a stainless barrel.
There are no barrels listed under the Blacktec's accessories tab so I asked the dealer to find out if it was possible to get the stainless one on a Blacktec model. They said they could for a surcharge of €190.00. I'm buying it from a German shop and they're exporting it to me. They said it would take 6 to 8 weeks to get the rifle from Walther, then I've to sort out the licencing and import/export paperwork. With the COVID restrictions this could take extra long - we'll see.