Anyone that wants to order a reusable RS-25 can have Aerojet Rocketdyne configure and manufacture it that way. See also the AR-22 variant used on the ill-fated DARPA XSP program.

The real issue with that engine isn't its reusability, it's that the industry has learned a lot about rocket engine design, operation, and manufacturing since the RS-25 was developed. That's reflected in the engines available from the likes of Blue Origin and SpaceX. No knock on the RS-25 - it stands as a watershed achievement for humanity in the engineering of thermodynamic systems.

Though calling the SpaceX engines "available" needs the caveat that SpaceX will not make them available outside of SpaceX.