question about building a pre-fab'ed engine

is this a thing? can i just buy an unassembled engine, and completely build it myself? i like the concept, it makes the car feel more connected to you, like a child, but without the constant whining and crying. but everywhere i look, i just cant seem to find anywhere? i saw a video of a guy build a bmw engine like this, everything oem, just rebuilt it. do i have to buy all the individual parts, or can i just got "hey ford, me want engine, hold the engine", and walk out with a big box