Here is the direct link to the HK listingsEFK has USPc threaded barrels on their site in stock right now. They are made from their own steel, but I hear they are pretty good. I'm thinking about purchasing one for myself. It's the only threaded barrel for the USPc I've been able to find. I emailed HKparts a couple months ago and they said they have some on order. They could be in stock sometime soon.
That's not possible, since the 'threaded barrel' is also extended...so the threads are actually useable for a suppressor or compensator...Get it threaded by tornado tech.