When I bought a car with a seized motor, I was able to find a replacement locally (Missouri) on nasioc midwest owners club. Often you can track some down on ebay. Also,
SILVERLINE AUTOMOTIVE
LEO AT 360-513-0663
and these guys:
Millennium Auto -Specializing in Subaru WRX STI
Two of the above vendors are typically involved at selling complete units, with everything attached. You might be able to get lucky and persuade one of them to sell you just a long block. Or buy the whole thing and sell off what you do not need.